Note: Descriptions are shown in the official language in which they were submitted.
CA 02841499 2014-01-27
COMPOSITIONS AND METHODS FOR PREVENTING STERNAL WOUND
INFECTIONS
BACKGROUND
Mediastinitis is an infection that results in swelling and inflammation of the
area between
the lungs containing the heart, large blood vessels, trachea, esophagus,
thymus gland, lymph
nodes, and connective tissues. Mediastinitis is a life-threatening condition
with an extremely
high mortality rate if recognized too late or treated improperly. Sternotomy
wounds become
infected in about 0.5% to about 9% of open-heart procedures and have an
associated mortality
rate of about 8% to about 15% despite flap closure. The rate of deep sternal
wound infection
(bone and mediastinitis) associated with median sternotomy ranges from about
0.5% to about 5%
and the associated mortality rate is as high as 22% independent of the type of
surgery performed.
Mediastinitis is classified as either acute or chronic. Chronic sclerosing (or
fibrosing)
mediastinitis results from long-standing inflammation of the mediastinum,
leading to growth of
acellular collagen and fibrous tissue within the chest and around the central
vessels and airways.
Acute mediastinitis usually results from esophageal perforation or median
sternotomy.
An esophageal perforation is a hole in the esophagus, the tube through which
food passes
from the mouth to the stomach. An esophageal perforation allows the contents
of the esophagus
to pass into the mediastinum, the surrounding area in the chest, and often
results in infection of
the mediastinum, i.e., mediastinitis. For patients with an early diagnosis,
e.g., less than 24 hours,
and a surgery that is accomplished within 24 hours, the survival rate is about
90%. However,
that rate drops to about 50% when treatment is delayed.
A median sternotomy is a surgical procedure in which a vertical inline
incision is made
along the sternum, after which the sternum itself is divided, or cracked. This
procedure provides
access to the heart and lungs for further surgical procedures such as a heart
transplant, correction
CA 02841499 2014-01-27
of congenital heart defects, or coronary artery bypass surgery. After the
surgery has been
completed, the sternum is usually closed with the assistance of wires or metal
tapes. The sternal
bony edges and gaps are subsequently covered and filled with a haemostatic
agent. The most
commonly used haemostatic agent is bone wax (bee's wax), despite the fact that
bone wax has
been reported to enhance infection, causes a foreign body reaction, and
inhibits bone growth
(Rahmanian et al, Am J Cardiol, 100(11): 1702-1708, 2007; Fakin et al., Infect
Control Hosp
Epidemiol 28(6):655-660, 2007; and Crabtree et al., Semin Thorac Cardiovasc
Surg., 16(1):53-
61, 2004).
The wound site, sternum and/or internal cavity can be contaminated with
bacteria at any
time during the surgery and closure. Whereas superficial sternal wound
infection may not in and
of itself be associated with high mortality rates, these infections can track
to the bony sternum
itself and cause osteomyelitis. Further tracking of infection into the
mediastinum results in
mediastinitis. Haemostatic agents such as bone wax are commonly employed to
provide a
physical barrier to entry of bacteria into and through the sternum, however,
their inflammatory
properties may actually enhance bacterial growth. More effective treatments
should employ
pharmacological as well as physical methods for preventing contamination of
the wound bed.
Although prophylactic antibiotics are the standard of care prior to most
surgical
procedures, IV antibiotics alone have not been very effective at reducing the
incidence of sternal
wound infection and mediastinitis. Also, there has been a growing concern of
antibiotic resistance
due to the absence of high local concentration at the sternal wound site
(Carson et al., J Am Coll
Cardiol, 40:418-423, 2002). Patients that develop deep chest surgical site
infection incur an
average cost of $20,927 more than non-infected patients, and incur an average
length of hospital
stay of twenty-seven days compared to five or six days for non-infected
patients.
Beginning in 2009, costs associated with treating acute mediastinitis will not
be covered
by Medicare. See Centers for Medicare & Medicaid Services Inpatient
Prospective Payment
System published in the Federal Register (Department of Health and Human
Services, 2007, Vol.
72, No. 162) on August 22, 2007.
There is, therefore, a need for compositions and methods for preventing
mediastinitis.
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CA 02841499 2014-01-27
SUMMARY OF THE INVENTION
The invention provides a topical composition including at least one antibiotic
agent for
application to an incision site in a patient having undergone a median
sternotomy or other
procedure in which the sternum is compromised. As used herein, topical refers
to a formulation
that is applied into, on top of, or in the interstices of a surface of a
subject, i.e., application to an
internal surface or an external surface of a subject. The surface can be a
surface of an internal
bone, an edge of a surgically cut internal bone, a surface of an internal
organ, a surface of an
internal muscle, or a surface of an incision site. In particular, topical
includes formulated for
application to the inside of the margins of a median sternotomy, i.e.,
application to the sternal
bony edges and gaps after a median sternotomy has been performed. Topical also
include
application to a surface of an esophageal perforation. Topical also includes
application to the
epidermis. Compositions of the invention may be made of any appropriate
material and are
preferably formulated as a paste, putty, cream, ointment, foam, or gel.
Application of
compositions of the invention in, for example, cardiac surgery, greatly
reduces infection leading
to mediastinitis.
An aspect of the invention provides an antimicrobial composition including at
least one
bioresorbable polymer, such as a tyrosine-derived polyesteramide and at least
one antimicrobial
agent, in which the composition is formulated for topical application to an
esophageal perforation
in a subject or a median sternotomy incision site in the subject, and in which
the antimicrobial
agent is present in an amount effective to inhibit bacterial colonization of
the site and/or
development of mediastinitis, a sternal wound infection, or a deep wound
infection in the subject.
In preferred embodiments, the composition is applied in between and on top of
the sternum of a
subject after closure using standard techniques. Topical formulations of such
compositions
include, but are not limited to, a putty, a paste, a gel, a foam, an ointment,
or a cream. In certain
embodiments, the composition further includes a binder.
Certain embodiments of these compositions further include an osteoinductive
agent.
Other embodiments of these compositions further include an osteoconductive
agent. Exemplary
bone-growth promoting substances include calcium phosphate, demineralized bone
matrix,
collagen, or hydroxyapatite.
In certain embodiments of these compositions, the binder is a polyalkyelene
oxide, for
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CA 02841499 2014-01-27
example polyethylene glycol (PEG) or polypropylene glycols, including
copolymers thereof. In
particular embodiments, the binder is PEG 400. In other embodiments, the
binder is a block
copolymer of polyethylene oxide (PEO) and polypropylene oxide (PPO), such as
Pluronic
triblock PEO/PPO copolymers available from BASF. In certain embodiments, the
compositions
herein are partially bioresorbable. In other embodiments, the compositions are
completely
bioresorbable.
Antimicrobial agents can include antibiotics, antiseptics, and disinfectants
that are
nontoxic and employable directly to internal organs. Exemplary antibiotic
agents include
tetracyclines, penicillins, macrolides, rifampin and combinations thereof. In
certain embodiments,
the composition includes a combination of antibiotic agents, such as
minocycline and rifampin.
In certain embodiments, compositions of the invention include a tyrosine-
derived
polyesteramide and at least one additional polymer selected from the group
consisting of
polylactic acid, polyglycolic acid, poly(L-lactide) (PLLA), poly(D,L-lactide)
(PLA) polyglycolic
acid [polyglycolide (PGA)], poly(L-lactide-co-D,L-lactide) (PLLA/PLA), poly(L-
lactide-co-
glycolide) (PLLA/PGA), poly(D, L-lactide-co-glycolide) (PLA/PGA),
poly(glycolide-co-
trimethylene carbonate) (PGA/PTMC), poly(D,L-lactide-co-caprolactone)
(PLA/PCL),
poly(glycolide-co-caprolactone) (PGA/PCL), poly(oxa)esters, polyethylene oxide
(PEO),
polydioxanone (PDS), polypropylene fumarate, poly(ethyl glutamate-co-glutamic
acid), poly(tert-
butyloxy-carbonylmethyl glutamate), polycaprolactone (PCL), polycaprolactone
co-
butylacrylate, polyhydroxybutyrate (PHBT), polyhydroxybutyrate,
poly(phosphazene),
poly(phosphate ester), poly(amino acid), polydepsipeptides,
polyiminocarbonates, poly[(97.5%
dimethyl-trimethylene carbonate)-co-(2.5% trimethylene carbonate)],
poly(orthoesters), tyrosine-
derived polycarbonates, tyrosine-derived
polyiminocarbonates, tyrosine-derived
polyphosphonates, polyethylene oxide, polyalkylene oxides, and
hydroxypropylmethylcellulose.
Another aspect of the invention provides a method of preventing mediastinitis,
sternal
wound infections, or deep wound infections in a subject, for example, a human,
in which one
applies an antimicrobial composition including a polymer and at least one
antimicrobial agent to
an esophageal perforation in a subject or a median sternotomy incision site in
the subject, in
which the at least one antimicrobial agent is present in an amount effective
to prevent
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CA 02841499 2014-01-27
development of mediastinitis, sternal wound infections, or deep wound
infections, in the subject.
By "preventing" mediastinitis, we mean substantially inhibiting microbial
growth (e.g. by
providing sufficient amounts of antimicrobial agents, as described herein, to
inhibit bacterial
growth) such that the incidence of mediastinitis is significantly reduced, for
example by at least
about 10%, for example, at least about 10%, at least about 20%, at least about
30%, at least about
40%, at least about 50%, at least about 60%, at least about 70%, at least
about 80%, at least about
90%, or at least about 95%.
In certain embodiments of the method, the composition further includes a
binder, for
example polyethylene glycol (PEG). In particular embodiments, the PEG is PEG
400. In other
embodiments of the method, the composition further includes an osteoinductive
agent. In other
embodiments of the method, the composition further includes an osteoconductive
agent. In
certain embodiments of the method, the polymer is a tyrosine-derived
polyesteramide. In certain
embodiments of the method, the polymer is a blend of at least two polymers. In
certain
embodiments of the method, the polymer is a blend of a tyrosine-derived
polyesteramide and at
least one additional polymer selected from the group consisting of: polylactic
acid, polyglycolic
acid, poly(L-lactide) (PLLA), poly(D,L-lactide) (PLA) polyglycolic acid
[polyglycolide (PGA)],
poly(L-lactide-co-D,L-lactide) (PLLA/PLA), poly(L-lactide-co-glycolide)
(PLLA/PGA), poly(D,
L-lactide-co-glycolide) (PLA/PGA), poly(glycolide-co-trimethylene carbonate)
(PGA/PTMC),
poly(D,L-lactide-co-caprolactone) (PLA/PCL), poly(glycolide-co-caprolactone)
(PGA/PCL),
poly(oxa)esters, polyethylene oxide (PEO), polydioxanone (PDS), polypropylene
fumarate,
poly(ethyl glutamate-co-glutamic acid), poly(tert-butyloxy-carbonylmethyl
glutamate),
polycaprolactone (PCL), polycaprolactone co-butylacrylate, polyhydroxybutyrate
(PHBT),
polyhydroxybutyrate, poly(phosphazene), poly(phosphate ester), poly(amino
acid),
polydepsipeptides, polyiminocarbonates, poly[(97.5% dimethyl-trimethylene
carbonate)-co-
(2.5% trimethylene carbonate)], poly(orthoesters), tyrosine-derived
polycarbonates, tyrosine-
derived polyim inocarbonates, tyrosine-derived polyphosphonates, polyethylene
oxide,
polyalkylene oxides, and hydroxypropylmethylcellulose.
In certain embodiments of the method, the polymer composition can be delivered
to the
patient in various forms. In certain embodiments, the composition is
formulated as a paste. In
other embodiments, the composition is formulated as a putty. Other exemplary
formulations
include a foam, a gel, an ointment, or a cream. In certain embodiments, the
composition is
5
CA 02841499 2015-06-25
partially bioresorbable. In other embodiments, the composition is completely
bioresorbable. In
other embodiments, the composition is bioresorbable and remodeled.
Another aspect of the invention provides a method of preventing mediastinitis
in a
subject, in which a putty comprising a tyrosine-derived polyesteramide, a
binder, and at least one
antimicrobial agent is applied to an esophageal perforation in a subject or a
sternotomy in the
subject, in which the at least one antimicrobial agent is present in an amount
effective to prevent
development of mediastinitis in the subject.
Another aspect of the invention relates to the use of a bioresorbable polymer
drug particle
as defined herein for inhibiting development of mediastinitis in a subject.
Another related aspect of the invention concerns the use of an antimicrobial
composition
as defined herein for inhibiting development of mediastinitis in a subject.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. I illustrates the rate of minocycline release from Ostene formulations.
Fig. 2 illustrates the rate of rifampin release from Ostene formulations.
Fig. 3 illustrates the rate of minocycline and rifampin release from Ostene -
P22-27.5
matrix formulations.
Fig. 4 illustrates the rate of minocycline and rifampin release from AIGIS
(TYRX
Pharma, Inc.).
DETAILED DESCRIPTION
The invention generally reLtes to compositions and methods for preventing
sternal
wound infections, deep wound infections, or mediastinitis. Mediastinitis is an
infection caused by
bacteria or fungi. The infection results in swelling and irritation
(inflammation) of the area
between the lungs (the mediastinum). Bacterial organisms and fungal organisms
refer to all
genuses and species of bacteria and fungi, including, for example, all
spherical, rod-shaped and
spiral bacteria. Exemplary bacteria are staphylococci (e.g., Staphylococcus
epidermidis and
Staphylococcus aureus), Enterrococcus faecalis, Pseudomonas aeruginosa,
Escherichia coli, other
gram-positive bacteria, and gram-negative bacilli. An exemplary fungus is
Candida albicans.
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CA 02841499 2015-06-25
Although mediastinitis is often polymicrobial, staphylococci are the most
common bacteria
colonized from infected patients.
In certain embodiments, the invention provides an antimicrobial composition
including at
least one bioresorbable polymer, such as a tyrosine-derived polyesteramide and
at least one
antimicrobial agent, in which the composition is formulated for topical
application to an
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6a
CA 02841499 2014-01-27
esophageal perforation in a subject or a median sternotomy incision site in
the subject, and in
which the at least one antimicrobial agent is present in an amount effective
to sterilize the sternal
wound site, i.e. prevent bacterial colonization of the wound site. In certain
embodiments, the
composition includes a binder.
As used herein, topical refers to a formulation that is applied into, on top
of, or in the
interstices of a surface of a subject, i.e., application to an internal
surface or an external surface of
a subject. The surface can be a surface of an internal bone, an edge of a
surgically cut internal
bone, a surface of an internal organ, a surface of an internal muscle, or a
surface of an incision
site. In particular, topical includes formulations for application to the
inside of the margins of a
median sternotomy, i.e., application to the sternal bony edges and gaps after
a median sternotomy
has been performed. Topical also include application to a surface of an
esophageal perforation.
Topical also includes application to the epidermis.
Antimicrobial Agents
Antimicrobial agents include antibiotics, antiseptics, and disinfectants. In
certain
embodiments, the antimicrobial composition includes only one of these agents.
In other
embodiments, the antimicrobial composition includes mixtures and combinations
of these agents,
for example, an antibiotic and an antiseptic, multiple disinfectants, or
multiple antibiotics, or
multiple antibiotics and multiple disinfectants, etc. In certain embodiments,
the antimicrobial
agents are soluble in organic solvents such as alcohols, ketones, ethers,
aldehydes, acetonitrile,
acetic acid, methylene chloride and chloroform.
Non-limiting examples of classes of antibiotics that can possibly be used
include
tetracyclines (e.g. minocycline), rifamycins (e.g. rifampin), macrolides (e.g.
erythromycin),
penicillins (e.g. nafeillin), cephalosporins (e.g. cefazolin), other 0-1actam
antibiotics (e.g.
imipenem, aztreonam), aminoglycosides (e.g. gentamicin), chloramphenicol,
sufonamides (e.g.
sulfamethoxazole), glycopeptides (e.g. vancomycin), quinolones (e.g.
ciprofloxacin), fusidic acid,
trimethoprim, metronidazole, clindamycin, mupirocin, polyenes (e.g.
amphotericin B), azoles
(e.g. fluconazole) and [beta]-lactam inhibitors (e.g. sulbactam).
Non-limiting examples of specific antibiotics that can be used include
minocycline,
rifampin, erythromycin, azithromycin, nafeillin, cefazolin, imipenem,
aztreonam, gentamicin,
sulfamethoxazole, vancomycin, ciprofloxacin, trimethoprim, metronidazole,
clindamycin,
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CA 02841499 2014-01-27
teicoplanin, mupirocin, azithromycin, clarithromycin, ofloxacin, lomefloxacin,
norfloxacin,
nalidixic acid, novobiocin, sparfloxacin, pefloxacin, amifloxacin, enoxacin,
fleroxacin,
temafloxacin, tosufloxacin, clinafloxacin, sulbactam, clavulanic acid,
amphotericin B,
fluconazole, itraconazole, ketoconazole, bacitracin, clindamycin, daptomycin,
lincomycin,
linezolid, metronid, polymyxin, rifaximin, vancomycin, triclosan,
chlorhexidine, sirolimus,
everolimus, and nystatin. Other examples of antibiotics, such as those listed
in Sakamoto et al.
(U.S. patent number 4,642,104), will readily suggest themselves to those of
ordinary skill in the
art.
Minocycline is a semi-synthetic antibiotic derived from tetracycline. It is
primarily
bacteriostatic and exerts its antimicrobial effect by inhibiting protein
synthesis. Minocycline is
commercially available as the hydrochloride salt which occurs as a yellow,
crystalline powder
and is soluble in water and slightly soluble in organic solvents including
alcohols, ketones, ethers,
aldehydes, acetonitrile, acetic acid, methylene chloride and chloroform.
Minocycline is active
against a wide range of gram-positive and gram-negative organisms.
Rifampin is a semi-synthetic derivative of rifamycin B, a macrocyclic
antibiotic
compound produced by the mold Streptomyces mediterranic. Rifampin inhibits
bacterial DNA-
dependent RNA polymerase activity and is bactericidal in nature. Rifampin is
commercially
available as a red-brown crystalline powder and is very slightly soluble in
water and freely
soluble in acidic aqueous solutions and organic solutions including alcohols,
ketones, ethers,
aldehydes, acetonitrile, acetic acid, methylene chloride and chloroform.
Rifampin possesses a
broad spectrum activity against a wide range of gram-positive and gram-
negative bacteria.
Novobiocin is an antibiotic obtained from cultures of Streptomyces niveus or
S.
spheroides. Novobiocin is usually bacteriostatic in action and appears to
interfere with bacterial
cell wall synthesis and inhibits bacterial protein and nucleic acid synthesis.
The drug also appears
to affect stability of the cell membrane by complexing with magnesium.
Novobiocin sodium is
freely soluble in water and alcohol. Novobiocin is available from The Upjohn
Company,
Kalamazoo, Mich.
Erythromycin is a macrolide antibiotic produced by a strain of Streptomyces
erythreaus.
Erythromycin exerts its antibacterial action by inhibition of protein
synthesis without affecting
nucleic acid synthesis. It is commercially available as a white to off-white
crystal or powder
8
CA 02841499 2014-01-27
slightly soluble in water and soluble in organic solutions including alcohols,
ketones, ethers,
aldehydes, acetonitrile, acetic acid, methylene chloride and chloroform.
Erythromycin is active
against a variety of gram-positive and gram-negative bacteria.
Nafeillin is a semi-synthetic penicillin that is effective against both
penicillin-G-sensitive
and penicillin-G-resistant strains of Staphylococcus aureus as well as against
pneumococcus,
beta-hemolytic streptococcus, and alpha streptococcus (viridans streptococci).
Nafeillin is readily
soluble in both water and organic solutions including alcohols, ketones,
ethers, aldehydes,
acetonitrile, acetic acid, methylene chloride and chloroform.
Examples of antiseptics and disinfectants are hexachlorophene, cationic
bisiguanides (e.g.
chlorhexidine, cyclohexidine) iodine and iodophores (e.g. povidone iodine),
para-chloro-meta-
xylenol, triclosan, furan medical preparations (e.g. nitrofurantoin,
nitrofurazone), methenamine,
aldehydes (glutaraldehyde, formaldehyde) and alcohols. Other examples of
antiseptics and
disinfectants will readily suggest themselves to those of ordinary skill in
the art.
Hexachlorophene is a bacteriostatic antiseptic cleansing agent that is active
against
staphylococci and other gram-positive bacteria. Hexachlorophene is soluble in
both water and
organic solutions including alcohols, ketones, ethers, aldehydes,
acetonitrile, acetic acid,
methylene chloride and chloroform.
These antimicrobial agents can be used alone or in combination of two or more
of them.
The antimicrobial agents can be dispersed throughout the polymer or in some
portion of the
polymer, e.g., tyrosine-derived polyesteramides. The amount of each
antimicrobial agent used
varies to some extent, but is at least of an effective concentration to
prevent development of
mediastinitis in a subject.
Tyrosine-Derived Polyesteramide
Non-limiting examples of tyrosine-derived polyesteramides include alternating
A-B type
copolymers consisting of a diphenol component and a dicarboxylic acid
component. The
dicarboxylic acids allow for variation in the polymer backbone while the
diphenols contain a
moiety for appending and varying a pendent chain.
The polyesteramides are based upon certain tyrosine-derived monomers, which
are co-
polymerized with a variety of dicarboxylic acids. The tyrosine-derived monomer
can be thought
9
CA 02841499 2014-01-27
of as a desaminotyrosyl tyrosine dipeptide in which the pendant carboxyl group
of the tyrosine
moiety has been esterified. The structure of one example of a suitable
tyrosine-derived monomer
is shown in Formula 1.
o
HO c,õ C¨NH¨CH¨CH2 gi OH
[1:1
Formula 1
In Formula 1, R is selected from the group consisting of: a straight or
branched chain
alkyl group containing up to 18 carbon atoms, an alkylaryl group containing up
to 18 carbon
atoms, a straight or branched chain alkyl group containing up to 18 carbon
atoms in which one or
more carbon atoms is substituted by an oxygen, and an alkylaryl group
containing up to 18
carbon atoms in which one or more carbon atoms is substituted by an oxygen.
In certain embodiments, R is a straight or branched chain alkyl group
containing 2-8
carbon atoms. In other embodiments, R is selected from the group consisting
of: methyl, ethyl,
propyl, butyl, isobutyl, sec-butyl, hexyl, octyl, 2-(2-ethoxyethoxy)ethanyl,
dodecanyl, and benzyl.
In still other embodiments, R is selected from the group consisting of: ethyl,
hexyl, and octyl. In
other embodiments, R is ethyl and k is 2.
One non-limiting example of a class of polyesteramides suitable for use in the
present
invention is formed by polymerizing the tyrosine-derived monomers of Formula 1
with the
diacarboxylic acids of Formula 2.
0 0
HO¨ El ¨OH
Formula 2
In Formula 2, Y is a saturated or unsaturated, substituted or unsubstituted
alkylene,
arylene, and alkylarylene group containing up to 18 carbon atoms. The
substituted alkylene,
arylene, and alkylarylene groups may have backbone carbon atoms replaced by N,
0, or S, or
may have backbone carbon atoms replaced by keto, amide, or ester linkages. Y
can be selected
CA 02841499 2014-01-27
so that the dicarboxylic acids are either important naturally-occurring
metabolites or highly
biocompatible compounds. In certain embodiments, dicarboxylic acids include
the intermediate
dicarboxylic acids of the cellular respiration pathway known as the Krebs
Cycle. These
dicarboxylic acids include a-ketoglutaric acid, succinic acid, fumaric acid,
malic acid and
oxaloacetic acid, for which Y is -CH2-CH2-C(=0)-, -CH2-CH2-, -CH=CH-, -CH2-CH(-
0H)-, and
-CH2-C(=0)-, respectively.
In particular embodiments, Y in Formula 2 is a straight chain alkylene group
having 2-8
carbons. In particular embodiments, Formula 2 is one of the following
dicarboxylic acid, succinic
acid, glutaric acid, diglycolic acid, adipic acid, 3-methyladipic acid,
suberic acid, dioxaoctadioic
acid and sebacic acid.
When polymerized, the tyrosine-derived monomers of Formula 1 and the
dicarboxylic
acids of Formula 2 give rise to polyesteramides that can be represented by
Formula 3.
0 0 0
11 11 11
tO H2t-C¨Nli ¨CH2 = C¨Y¨C-
---0
k=1,2
(!)1( ¨
Formula 3
where R and Y are as described above. In this formula, as in other formulas
herein, an
"n" outside brackets or parentheses, and having no specified value, has its
conventional role in the
depiction of polymer structures. That is, "n" represents a large number, the
exact number
depending on the molecular weight of the polymer. This molecular weight will
vary depending
upon the conditions of formation of the polymer.
A particular subset of the polyesteramides of Formula 3 is the subset where k
= 2 and
both R and Y are straight chain alkyl groups. This polyesteramide subset can
be represented by
Formula 4.
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CA 02841499 2014-01-27
0 0
111 411
=0
0
1th
Formula 4
In Formula 4, b = 1-17 and c = 1-18. In certain embodiments, b = 1-7 and c = 2-
8.
A polyesteramide for use in the present invention is the polyesteramide of
Formula 4
where b = 1 and c = 2. This polyesteramide is referred to herein as p(DTE
succinate). This name
illustrates the nomenclature used herein, in which the names of
polyesteramides are based on the
monomers making up the polyesteramides. The "p" stands for polymer; the "DTE"
stands for
Desaminotyrosyl Tyrosine Ethyl ester; the "succinate" refers to the identity
of the dicarboxylic
acid. p(DTE succinate) is formed by the polymerization of the tyrosine-derived
monomer
desaminotyrosyl tyrosine ethyl ester and the dicarboxylic acid succinic acid.
Another polyesteramide for use in the present invention contains three monomer
subunits: desaminotyrosyl tyrosine ethyl ester, succinic acid, and
desaminotyrosyl tyrosine. The
monomer desaminotyrosyl tyrosine (referred to herein as "DT") is the same as
desaminotyrosyl
tyrosine ethyl ester except that it contains a pendant free carboxylic acid
group rather than the
pendant ethyl ester of desaminotyrosyl tyrosine ethyl ester.
Inclusion of a certain percentage of desaminotyrosyl tyrosine monomers in the
polymer
produces a polyesteramide with that certain percentage of free carboxylic acid
groups in the
pendant chains. The structure of the polyesteramide corresponding to p(DTE
succinate) but
having free carboxylic acid groups in the pendant chains can be represented by
Formula 5.
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CA 02841499 2014-01-27
=
, =
*
t):
4 * = , = * = , le , I ,M * 4 =
Formula 5
In Formula 5, or for any polymer having tyrosine-derived diphenol free acid
moieties and
tyrosine-derived diphenol ester moieties, "a" is a number between 0.01 and
0.99 that represents
the mole fraction of tyrosine-derived monomer that is esterified, i.e.,
without a free carboxylic
acid group. It is understood that the depiction of the tyrosine-derived
monomers without and with
free carboxylic acid groups as alternating in Formula 5 is for the sake of
convenience only.
Actually, the order in which tyrosine-derived monomers without free carboxylic
acid groups and
tyrosine-derived monomers with free carboxylic acid groups appear in the
polyesteramide
generally will be random, although the overall ratio in which these two
monomers appear will be
governed by the value of "a". Exemplary values of "a" include: 0.97, 0.96,
0.95, 0.94, 0.93, 0.92,
0.91, 0.90, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, 0.82, 0.81, and 0.80,
0.75, 0.70, 0.65, 0.60 and
0.55. Ranges for "a" also include 0.95-0.60, 0.90-0.70, and 0.95-0.75
The presence of free carboxylic acid groups and percentage of these groups is
indicated
in the nomenclature used herein by modifying the name of the polyesteramide in
the manner
illustrated for p(DTE succinate) as follows: p(5% DT, DTE succinate) indicates
p(DTE succinate)
with 5% free carboxylic acid groups, p(10% DT, DTE succinate) indicates p(DTE
succinate) with
10% free carboxylic acid groups, p(15% DT, DTE succinate) indicates p(DTE
succinate) with
15% free carboxylic acid groups, etc.
Another polyesteramide for use in the present invention is p(DTE adipate).
p(DTE
adipate) is formed by the polymerization of the tyrosine-derived monomer
desaminotyrosyl
tyrosine ethyl ester and adipic acid. Another polyesteramide is p(DTE adipate)
in which some of
the pendant groups are free carboxylic acid groups, e.g., p(10% DT, DTE
adipate), p(15%
DT,DTE adipate), etc.
In general, any of the polyesteramides employed in the present invention can
contain any
13
CA 02841499 2014-01-27
desired percentage of pendant groups having free carboxylic acid groups. Thus,
the present
invention includes compositions of matter in which at least one antimicrobial
agent is embedded,
dispersed, or dissolved in a polyesteramide polymer matrix in which the
polyesteramide polymer
has the structure shown in Formulas 3 or 4 except that a certain percentage of
the pendant chains
are free carboxylic acid groups rather than esters. The structure of the
polyesteramide polymer
similar to Formula 3, but having free carboxylic acid groups in the pendant
chains is shown in
Formula 6.
¨14H * 0...g.. === y
koi,2
kola
Formula 6
In Formula 6, R and Y are as in Formula 3. Usually, both instances of Y will
be the same
but this does not have to be the case, "a" is as defined above for Formula 5.
The structure of the polyesteramide polymer similar to Formula 4, but having
free
carboxylic acid groups in the pendant chains can be represented by Formula 7.
. a o
Formula 7
In Formula 7, "b" and "c" are as in Formula 3. Usually, both instances of "c"
will be the
same. Exemplary values of "b" include 1, 5, and 7; exemplary values of "c"
include 2, 4, 6, and 8.
Values of "a" are as defined in Formula 5.
The incorporation of free carboxylic acid groups in the polyesteramides has
the effect of
accelerating the rate of polymer degradation and resorption when the
polyesteramides are placed
in physiological conditions, e.g., implanted into or applied to the body of a
patient, as in a
surgical incision site or a wound site. The presence of the free carboxylic
acid groups also
affects the behavior of the polyesteramide in response to pH.
Polyesteramides having a
14
CA 02841499 2014-01-27
relatively high concentration of pendent carboxylic acid groups are stable and
water insoluble in
acidic environments but dissolve or degrade rapidly when exposed to neutral or
basic
environments. By contrast, copolymers of low acid to ester ratios are more
hydrophobic and will
not degrade or resorb rapidly in either basic or acidic environments.
Such characteristics imparted by the carboxylic acid groups allow for the
production of
drug delivery devices including polyesteramides and at least one antimicrobial
agent that is
tailored to degrade or be resorbed at predetermined rates, and to deliver
predetermined amounts
of at least one antimicrobial agent at predetermined rates, by choosing the
proper percentage of
carboxylic acid groups in the polyesteramide. In particular embodiments, the
percentage of
pendant chains that are free carboxyl groups in the polyesteramide polymers
used in the present
invention is about 1-99%, 5-95%, 10-80%, 15-75%, 20-50%, or 25-40%. In
particular
embodiments, the percentage of pendant chains that are free carboxyl groups is
about 1%, 2%,
3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%,
20%,
21%, 22%, 23%, 24%, 25%, 30%, 35%, or about 40%.
Further polymers that can be used in the present invention are co-polymers of
the
tyrosine-based polyesteramides described above and poly(alkylene oxides).
These co-polymers
are random block copolymers of a dicarboxylic acid with a tyrosine-derived
diphenol and a
poly(alkylene oxide), in which an equimolar combined quantity of the diphenol
and the
poly(alkylene oxide) is reacted with the dicarboxylic acid in a molar ratio of
the diphenol to the
poly(alkylene oxide) between about 1 :99 and about 99: 1 to give a polymer
having the following
structure:
= 40 &I-1m
14*
Formula 8
where R4 is -CH=CH- or (-CH2-), in which "j" is between 0 and 8, inclusive; R5
is selected from
the group consisting of straight and branched alkyl and alkylaryl groups
containing up to 18
CA 02841499 2014-01-27
carbon atoms and optionally containing at least 1 ether linkage; R6 is
selected from the group
consisting of saturated and unsaturated, substituted and unsubstituted
alkylene, arylene and
alkylarylene groups containing up to 18 carbon atoms; each R7 is independently
an alkylene
group containing up to 4 carbon atoms; "x" is between about 5 and about 3,000;
and "f' is the
percent molar fraction of alkylene oxide in the copolymer and ranges between
about 1 and about
99 mole percent.
In certain embodiments, R4 is ethylene; R5 is ethyl; R6 is ethylene or
butylene; R7 is
ethylene; and all substituents on the benzene rings in the polymer backbone
are in the para
position.
The poly(alkylene oxide) monomer used to produce the polymer shown in Formula
8 can
be any commonly used alkylene oxide known in the art, for example a
poly(ethylene oxide),
poly(propylene oxide), or poly(tetramethylene oxide). Poly(alkylene oxide)
blocks containing
ethylene oxide, propylene oxide or tetramethylene oxide units in various
combinations are also
possible constituents within the context of the current invention.
1 5 In
certain embodiments, the poly( alkylene oxide) can be a poly(ethylene oxide)
in which
"x" of Formula 8 is between about 10 and about 500, or about 20 and about 200
. In certain
embodiments, poly(ethylene oxide) blocks with a molecular weight of about
1,000 to about
20,000 g/mol are used.
Tyrosine-based polyesteramides also include polyesteramides that are formed
from
aminophenol esters, e.g., tyrosine esters and the like, and diacids in the
manner described below.
These polymers can incorporate both free acid side chains and esterified side
chains. Exemplary
tyrosine-based polyesteramides of this type include one or more repeating
units represented by
fo,'%"11
0 0
¨R y
'L. s
COOR
Formula 9
in which: R is (CR3R4)a or -CR3=CR4-; R1 is hydrogen; saturated or unsaturated
alkyl, aryl,
alkylaryl or alkyl ether having from 1 to 20 carbon atoms; or
(R5)0((CR3R4)r0)s-R6; R2 is
independently a divalent, linear or branched, substituted or unsubstituted
alkyl, alkenyl, alkynyl,
16
CA 02841499 2014-01-27
aryl, alkylaryl, alkyl ether or aryl ether moiety having from 1 to 30 carbon
atoms;
(R5)0((CR3R4),0),(R5)q; or (RAICO2((CR3R0r0)sCO(R5)q; R3 and R4 are
independently,
hydrogen or linear or branched, substituted or unsubstituted alkyl having from
1 to 10 carbon
atoms; R5 is independently linear or branched, lower alkylene or lower
alkenylene; R6 is
independently linear or branched, substituted or unsubstituted, saturated or
unsaturated lower
alkyl; the aromatic ring has from zero to four Z1 substituents, each of which
is independently
selected from the group consisting of halide, lower alkyl, alkoxy, nitro,
alkyl ether, a protected
hydroxyl group, a protected amino group and a protected carboxylic acid group;
Y is
zt 000%21
R¨ R2
¨o¨eY1¨a¨
or COORt
a is 0 to 10; each q is independently 1 to 4; each r is independently 1 to 4;
and each s is
independently 1 to 5000.
These polymers are biodegradable polymers having atninophenol units and diacid
units
that can be generally represented by the formula p(-AP-X-)n, in which n is the
actual number or
the weight average number of repeat units in the polymer. In one embodiment,
the aminophenols
(AP) have the structure shown in Formula 10
RCH¨NH2
1107µr
cooR,
Formula 10
and the diacids (X) have the structure shown in Formula 11.
0 0
140¨c¨Rf-g--OH
Formula 11
When these monomeric units are polymerized under condensation conditions (or
other
precursors depending on the synthesis route), the resultant polymers have
backbones with both
ester and amide bonds, and side chains with ester or free acids (depending on
the choice of R1).
While the repeat motif of the polymer has the structure AP-X, this simple
representation of the
polymer does not reflect the various coupling permutations of the aminophenol
and the diacid,
17
CA 02841499 2014-01-27
i.e., whether the coupling between the aminophenol and the diacid occurs via
reaction of the AP's
amine functional group with one of the acid groups to produce an amide linkage
or via the
reaction of the AP's hydroxyl functional group with one of the acid groups to
produce an ester
linkage. Hence, the AP-X repeat unit can be represented by the either
structure below
("repeat a" or "repeat b", respectively).
zi exi.Zi
¨00-- 0
0
100R1 .1
repeat a repeat b
This simple structural representation (-AP-X-) does not show the relative
relationship of
these units to one another since these units can be further joined together by
either an amide or
ester bond. Hence, the actual structures of the polymers of the present
invention which contain
the aminophenol and diacid moieties described herein depend on the choice of
synthetic route, the
choice of coupling agents and the selective reactivity in forming amide or
ester bonds.
Accordingly, these tyrosine-based polyesteramides are random copolymers of
repeats a
and b or strictly alternating copolymers of repeat a, repeat b or both repeats
a and b, with the
particular polymer structure determined by the method of synthesis as
described herein.
Random copolymers of repeats a and b, are denominated by the simple formula
p(-AP-X-), AP-X or as random ab polymers, such names being used
interchangeably. Names for
this polymer class are based on these representations so that random ab
polymers are named for
the aminophenol moiety followed by the diacid moiety, regardless of the
starting materials. For
example, a polymer made by random copolymerization of tyrosine ethyl ester
(TE) as the
aminophenol moiety with succinic acid as the diacid moiety is referred to as
p(TE succinate) or
TE succinate. If the diacid moiety were changed to glutaric acid, this random
copolymer would
be p(TE glutarate) or TE glutarate. For additional clarity or emphasis, the
word random may be
appended to the polymer name, e.g., TE succinate random or p(TE succinate)
random. If the
polymer is designated without anything after the name, then the polymer is a
random copolymer.
There are two strictly alternating copolymers classes that can be obtained
from these
monomeric units: (1) a linear string of a single repeat, either "repeat a,"
thus in format (a)n or
"repeat b," thus in format (b)õ, which are equivalent formats; or (2) a linear
string of alternating
18
CA 02841499 2014-01-27
"repeat a" and "repeat b," thus in form (ab),, or (ba)n, which are equivalent
representations for
these polymers. In all cases, n is the number of repeat units. For polymers, n
is usually
calculated from the average molecular weight of the polymer divided by the
molecular weight of
the repeat unit.
Strictly alternating polymers of the (a),, form are referred to as p(-0-AP-X-)
or as
alternating "a" polymers. Alternating "a" polymers occur when the reaction
conditions are such
that the free amine of the aminophenol reacts first with the diacid (or other
appropriate reagent) as
controlled by the reaction conditions, forming an amide linkage and leaving
the hydroxyl free for
further reaction. For example, a polymer made by copolymerization of tyrosine
ethyl ester (TE)
as the aminophenol moiety with succinic anhydride (to provide the diacid
moiety) leads to an
alternating "a" polymer and is referred to herein as p(0-TE succinate) or 0-TE
succinate.
Polymers of the (ab),, form are referred to as p(-AP-Xi-AP-X2-), p(AP-Xi -AP-
X2) or as
AP-X1-AP-X2, when having "a" and "b" repeats with different diacids or as "p(-
AP-X-)
alternating" or as "AP-X alternating", when the "a" and "b" repeats have the
same diacid.
Polymers with two different diacids can be made, for example, by reacting two
equivalents of an aminophenol with one equivalent of a first diacid under
conditions that favor
amide bond formation and isolating the reaction product, a compound having the
structure
AP-X1-AP, which is also referred to herein as a trimer because it consists of
two aminophenol
units and one diacid unit. This trimer is reacted with a second diacid under
polymerization
conditions to produce the polymer p(-AP-Xi-AP-X2-) if the second diacid is
different from the
first diacid, or to produce the polymer p(-AP-X-) alternating if the second
diacid is the same as
the first diacid. As an illustration, an initial trimer made from TE and
succinic acid is
denominated as TE-succinate-TE. Reaction of TE-succinate-TE with glutaric acid
produces the
polymer p(TE-succinate-TE glutarate), whereas reaction with succinic acid
produces the polymer
p(TE succinate) alternating.
The polymers of the invention also include polymers made with mixed
aminophenol
repeats, mixed diacid repeats and mixed trimer repeats, or any combination of
such mixtures.
For these complex polymers, the mixed moiety is designated by placing a colon
between the
names of the two moieties and indicating the percentage of one of the
moieties. For example,
19
CA 02841499 2014-01-27
p(TE:10TBz succinate) random is a polymer made by using a mixture of 90%
tyrosine ethyl
ester and 10% tyrosine benzyl ester with an equimolar amount of the diacid
succinic acid under
random synthesis conditions. An example of a strictly alternating (ab)õ
polymer with a mixed
second diacid is p(TE-diglycolate-TE 1 OPEG-bis-succinate:adipate). This
polymer is made by
preparing the TE-diglycolate-TE trimer and copolymerizing it with a mixture of
10% PEG-bis-
succinic acid and 90% adipic acid. An example of a strictly alternating (ab),,
polymer with mixed
trimers is p(TE-succinate-TE:35TE- glutarate-TE succinate). This polymer is
made by
conducting a separate synthesis for each trimer, mixing the isolated trimers
in the indicated ratio
(65:35 succinate: glutarate) and copolymerizing with an equimolar amount of
succinic acid. With
such complexity, it is often simpler to list the various components and
relative amounts in a
table, especially for strictly alternating (ab)õ polymers. Table 1 provides
examples of some
strictly alternating (ab),, polymers. In Table 1, Tg is the glass transition
temperature of the
polymer after synthesis. Mol. Wt. is the molecular weight of the polymer after
synthesis as
determined by gel permeation chromatography.
Examples of tyrosine-based polyesteramides include, but are not limited to,
those shown
in Table 1 as well as polymers (1) wherein the aminophenol unit in the polymer
is provided by a
tyrosine ester such as tyrosine methyl ester, tyrosine ethyl ester, tyrosine
benzyl ester, free
tyrosine, or a methyl, ethyl, propyl or benzyl ester of 4-hydroxyphenylglycine
as well as 4-
hydroxyphenylglycine, and (2) wherein the diacid unit is succinic acid,
glutaric acid, adipic acid,
diglycolic acid, dioxaoctanoic acid, a PEG acid or a PEG bis-diacid (e.g., PEG-
bis-succinate or
PEG-bis-glutarate).
CA 02841499 2014-01-27
Table 1
First Trimer % Second % First ¨ % Second
%
AP-Xi-AP ist Ter 2d X2 diacid 1st .X.,2 diacid 2d
('C) Wt.
AP-Xi-AP
SkDal.
TE-diglycolate- 100 PEG600 25 Glutaric 75 25 111
TE Acid acid
Tglycolate- 100 PEG400- 25 Olutaric 73 29 130
TE bis- acid
succinate
TE-succinate- 65 TE- 35 Succinic 100 32 120
TE (PE0400- acid
succinate)-
TE
TE-glutarate- 100 P0400- 33 Succinic 65 28 190
TE bis- acid
___________________________________ succinate
TE7g1 Utaillte. 100 PEG400- 35 Glutaric 65
26 199
TE bis- acid
succinate
TE-glutarate- 100 Glutaric 100 70 74
TE acid
For polymers with mixed aminophenol repeats, the polymer contains from about
5% to
about 40% or from about 10% to about 30% of a first aminophenol repeat with
the remainder
being the second aminophenol repeat. For polymers with mixed diacid repeats,
the polymer
contains from about 10% to about 45% or from about 20% to about 40% of a first
diacid repeat
with the remainder being the second diacid repeat. For polymers with mixed
trimer repeats, the
polymer contains from about 5% to about 40% or from about 10% to about 30% of
a first trimer
with the remainder being the second trimer. Polymers made from any and all of
the foregoing
possible permutations are contemplated by the present invention. Additional
examples of specific
polymers of the invention include p(TE succinate), p(TE succinate)
alternating, p(TE glutarate),
p(TE glutarate) alternating, p(TE diglycolate),p(TE diglycolate) alternating,
p(TE: 15T glutarate),
Tg 78, Mol. wt. 74 kDa; and p(TE:15TBz glutarate). This last polymer is an
example of an
intermediate polymer used in preparation of p(TE: 15T glutarate).
Other tyrosine-based polyesteramides include those in which a strictly
alternating
21
CA 02841499 2014-01-27
polymer has been synthesized with a trimer selected from the group consisting
of TE-succinate-
TE, TE-glutarate-TE, TE-adipate-TE, TE-diglycolate-TE, and TE-X-TE monomers
wherein X is
comprised of a PEG unit with or without other species, such as a PEG
bifunctionalized via
condensation with two equivalents of a diacid such as succinic acid, glutaric
acid, adipic acid,
diglycolic acid, or others . Any of these trimers can be copolymerized with a
diacid repeat
selected from the group of succinic acid, glutaric acid, adipic acid,
diglycolic acid,
dioxaoctandioic acid, a PEG acid and a PEG bis-diacid (e.g., PEG-bis-succinate
and PEG-bis-
glutarate), or any mixture of these diacids or other diacids.
Because of the bifunctionality of the aminophenol and the diacid, the basic
monomeric
unit (here arbitrarily designated as repeat a), can add either another of
"repeat a" or add "repeat b"
as the subsequent monomeric unit. Accordingly, the variable Y reflects this
and is defined as
"repeat a" with the amide bond (below left) or "repeat b" with the ester bond
(below right).
Zt ZI
I 0
0 0
LORI Ikke)
For a random polymer each subsequent Y would be randomly either "repeat a" or
"repeat
b." For a strictly alternating (a)n polymer, Y would always be "repeat a". For
a strictly alternating
(ab),, polymer, Y would always be "repeat b".
The values of each "a" are independently 0 or one of the whole numbers 1-10.
When "a"
is zero, the corresponding group is omitted and a single carbon bond is
present. The value of each
"q" and "r" is independently one of the whole numbers 1, 2, 3 or 4.
The value of each "s" is independently about 1 to about 5000 and determines
the number
of repeat units in the alkylene oxide chain. Hence, "s" can range from 1 or
from 5 to about 10, to
about 15, to about 20, to about 30, to about 40, to about 50, to about 75, to
about 100, to about
200, to about 300, to about 500, to about 1000, to about 1500, to about 2000,
to about 2500, to
about 3000, to about 4000 and to about 5000. Additionally, when the length of
the alkylene oxide
chain is stated as a molecular weight, then "s" need not be a whole number but
can also be
expressed as a fractional value, representative of the average number of
alkylene oxide repeating
units based on the cited (or a measured) molecular weight of the poly(alkylene
oxide).
22
CA 02841499 2014-01-27
The tyrosine-based polyesteramides can be homopolymers or copolymers. To
create
heteropolymers (or copolymers), as also described above in context of polymer
nomenclature,
mixtures of the aminophenol and/or the diacid (or appropriate starting
materials) can be used to
synthesize the polymers of the invention.
When the polymers are copolymers, they contain from at least about 0.01% to
100% of
the repeating monomer units, from at least about 0.05%, 0.1%, 0.5%, 1%, 2%,
3%, 4%, 5%, 6%,
8%, 10%, 12%, 15% to about 30%, 40%, 50%, 60%, 75%, 90%, 95% or 99% in any
combination
of ranges. In certain embodiments, the range of repeating units in free acid
form on the
aminophenol moiety of the polymer is from about 5% to about 50%, i.e., R1 is H
- prepared via an
intermediate in which Ri is benzyl, with the remaining R1 groups being alkyl
or other ester stable
to hydrogenolysis. In certain embodiments, the range of free acid is from
about 5% to about 40%,
including about 5%, about 10%, about 15%, about 20%, about 25%, about 30%,
about 35%, and
about 40%, inclusive of all ranges and subranges there between. In other
embodiments, the free
acid ranges from about 10% to about 15%, about 10% to about 20%, about 10% to
about 25%,
about 10% to about 30%, and about 10% to about 35%.
Alternatively or additionally, the copolymers can have varying ratios of the
diacid
moiety, so that mixtures have from about 20% to about 80% of at least one
diacid described
herein. In certain embodiments of the invention, the copolymers are a mixture
of two or more
diacids as described herein. In certain embodiments, mixed diacids are
combinations of various
alkylene oxide type moieties, such as PEG acids or PEG-bis-alkyl acids or
combinations of those
alkylene oxide type moieties with other diacids, especially small, and
naturally-occurring,
diacids such as succinic acid, glutaric acid, adipic acid and diglycolic acid.
For alkylene oxide
mixtures, the mixture contains from about 20%, 25%, 30%, 35%, 40%, 45% to
about 50% of one
alkylene oxide. In certain embodiments, the mixture is about 50% of each
alkylene oxide.
For alkylene oxide-other diacid mixtures, the mixture contains from about 20%,
25%, 30%, 35%,
40%, 45% or 50% of the alkylene oxide, with the remainder being the other
diacid. In yet
another embodiment, the amount of the alkylene oxide is about 20% to about
40%.
Further, the ester moiety of the aminophenol can be varied by using alkyl
esters or
another class of esters such as alkylaryl esters, or esters with alkylene
oxide chains or ether
chains, or another compatible functional group. To have this ester moiety
converted to a free
23
CA 02841499 2014-01-27
acid, the polymer can be synthesized using a benzyl ester (or other easily
hydrolyzable moiety)
which can be removed by hydrogenolysis as described in U.S. Patent No.
6,120,491 or by other
technique that preferentially removes the benzyl group without hydrolyzing the
backbone of the
polymer. Hence, the polymers of the invention can be made with mixtures of
aminophenol and
diacids that have variability among the different substituents, i.e.,
differences can reside at any of
R, R1-R10, Zi or the other variables of the repeat units. Finally, the other
monomer units in the
copolymer can be substantially different provided such moieties preserve the
properties of the
polymer and are capable of copolymerizing to form polymers with aminophenol
and diacid
moieties.
While many biodegradable tyrosine-derived polyesteramides are specifically
illustrated
above, further such polymers for use in the invention are described in U.S.
Patent Numbers
5,099,060; 5,216,115; 5,317,077; 5,587,507; 5,658,995; 5,670,602; 6,048,521;
6,120,491;
6,319,492; 6,475,477; 6,602,497; 6,852,308; 7,056,493; RE37,160E; and
RE37,795E; as well as
those described in U.S. patent application publication numbers 2002/0151668;
2003/0138488;
2003/0216307; 2004/0254334; 2005/0165203, 2009/0088548, 2010/0129417,
2010/0074940;
those described in PCT publication numbers W099/52962; WO 01/49249; WO
01/49311; and
WO 03/091337.
The tyrosine-derived diphenol compounds used to produce the polyesteramides
suitable
for use in the present invention can be produced by known methods such as
those described in,
e.g., U.S. patent numbers 5,099,060 and 5,216,115. The production of
desaminotyrosyl tyrosine
ethyl ester, desaminotyrosyl tyrosine hexyl ester, and desaminotyrosyl
tyrosine octyl ester can
also be carried out by known methods, see, e.g., Pulapura & Kohn, 1992,
Biopolymers 32:411-
417 and Pulapura et al., 1990, Biomaterials 11:666-678. The dicarboxylic acids
are widely
available from a variety of commercial sources.
A tyrosine-derived diphenol monomer and a dicarboxylic acid may be reacted to
form a
polyesteramide suitable for use in the present invention according to the
methods disclosed in
U.S. patent number 5,216,115. According to these methods, the diphenol
compounds are reacted
with the dicarboxylic acids in a carbodiimide-mediated direct
polyesterification using 4-
(dimethylamino)pyridinium-p-toluene sulfonate (DPTS) as a catalyst to form the
polyesteramides. Random block copolymers with poly(alkylene oxide) according
to Formula 8
24
CA 02841499 2014-01-27
may be formed by substituting poly(alkylene oxide) for the tyrosine derived
diphenol compound
in an amount effective to provide the desired ratio of diphenol to
poly(alkylene oxide) in the
random block copolymer.
C-terminus protected alkyl and alkylaryl esters of tyrosine containing up to 8
carbon
atoms can be prepared according to the procedure disclosed in J. P. Greenstein
and M. Winitz,
Chemistry of the Amino Acids, (John Wiley & Sons, New York 1961), p. 929. C-
terminus
protected alkyl and alkylaryl esters of tyrosine containing more than 8 carbon
atoms can be
prepared according to the procedure disclosed in U.S. patent number 4,428,932.
N-terminus protected tyrosines can be prepared following standard procedures
of peptide
chemistry such as disclosed in Bodanszky, Practice of Peptide Synthesis
(Springer- Verlag, New
York, 1984).
Crude tyrosine derivatives are sometimes obtained as oils and can be purified
by simple
recrystallization. Crystallization of the pure product is accelerated by
crystal seeding.
The diphenols can then be prepared by carbodiimide-mediated coupling reactions
in the
presence of hydroxybenzotriazide following standard procedures of peptide
chemistry such as
disclosed in Bodanszky, Practice of Peptide Synthesis (Springer- Verlag, New
York, 1984) at
page 145. The crude diphenols can be recrystallized twice, first from 50%
acetic acid and water
and then from a 20:20: 1 ratio of ethyl acetate, hexane, and methanol, or,
alternatively, by flash
chromatography on silica gel, employing a 100:2 mixture of methylene
chloride:methanol as the
mobile phase. Desaminotyrosyl tyrosine esters also can be prepared by the
carbodiimide mediated
coupling of desaminotyrosine and tyrosine esters in the presence of
hydroxybenzotriazole.
The diphenol compounds can then be reacted with dicarboxylic acids in a
carbodiimide-
mediated direct polyesterification using 4-(dimethylamino)pyridinium-p-toluene
sulfonate
(DPTS) as a catalyst to form polyesteramides.
Because the diphenols of the present invention are base-sensitive, the
polyesteramides of
the present invention are prepared by direct polyesterification, rather than
by dicarboxylic acid
chloride techniques. Polyesterification condensing agents and reaction
conditions should be
chosen that are compatible with the base-sensitive diphenol starting
materials. Thus, the
CA 02841499 2014-01-27
polyesteramides can also be prepared by the process disclosed by Ogata et al,
1981, Polym. J.,
13:989-991 and Yasuda et al, 1983, J. Polym. Sci: Polym. Chem. Ed., 21:2609-
2616 using
triphenylphosphine as the condensing agent; the process of Tanaka et al, 1982,
Polym. J.
14:643 648 using picryl chloride as the condensing agent; or by the process of
Higashi et al,
1986, J. Polym. Sci: Polym. Chem. Ed. 24:589-594 using phosphorus oxychloride
as the
condensing agent with lithium chloride monohydrate as a catalyst.
The polyesteramides can also be prepared by the method disclosed by Higashi et
al.,
1983, J. Polym. Sci.: Polym. Chem. Ed. 21:3233-3239 using arylsulfonyl
chloride as the
condensing agent; by the process of Higashi et al., 1983, J. Polym. Sci.:
Polym. Chem. Ed.
21:3241-3247 using diphenyl chlorophosphate as the condensing agent; by the
process of Higashi
et al., 1986, J. Polym. Sci.: Polym. Chem. Ed. 24:97-102 using thionyl
chloride with pyridine as
the condensing agent; or by the process of Elias, et al., 1981, Makromol.
Chem. 182:681-686
using thionyl chloride with triethylamine. An additional polyesterification
procedure is the
method disclosed by Moore et al., 1990, Macromol. 23:65-70 utilizing
carbodiimide coupling
reagents as the condensing agents with the specially designed catalyst 4-
(dimethylamino)pyridinium-p-toluene sulfonate (DPTS). A particular
polyesterification technique
modifies the method of Moore to utilize an excess of the carbodiimide coupling
reagent. This
produces aliphatic polyesteramides having molecular weights greater than those
obtained by
Moore. When carbodiimides are used in peptide synthesis as disclosed by
Bodanszky, Practice of
Peptide Synthesis (Springer- Verlag, New York, 1984), between 0.5 to 1.0 molar
equivalents of
carbodiimide reagent is used for each mole of carboxylic acid group present.
In the preferred
methods disclosed herein, greater than 1.0 molar equivalents of carbodiimide
per mole of
carboxylic acid group present are used. This is what is meant by describing
the reaction mixture
as containing an excess of carbodiide.
Essentially any carbodiimide commonly used as a coupling reagent in peptide
chemistry
can be used as a condensing agent in the polyesterification process. Such
carbodiimides are
well-known and disclosed in Bodanszky, Practice of Peptide Synthesis (Springer-
Verlag, New
York, 1984) and include dicyclohexylcarbodi imide, di isopropylcarbodiimide, 1-
(3-
dimethylaminopropy1)-3-ethyl carbodiimide hydrochloride, N-
cyclohexyl-N'-(2'-
morpholinoethyl)carbodiimide-metho-p-toluene sulfonate, N-
benzyl-N'-3'-
dimethylaminopropyl-carbodiimide hydrochloride, 1-
ethy1-3-(3-
26
CA 02841499 2014-01-27
dimethylaminopropyl)carbodiimide methiodide, N-ethylcarbodiimide
hydrochloride, and the like.
In certain embodiments, the carbodiimides are dicyclohexyl carbodiimide and
di isopropylcarbodiimide.
A reaction mixture is formed by contacting equimolar quantities of the
diphenol and the
dicarboxylic acid in a solvent for the diphenol and the dicarboxylic acid.
Suitable solvents include
methylene chloride, tetrahydrofuran, dimethylformamide, chloroform, carbon
tetrachloride, and
N-methyl pyrrolidinone. It is not necessary to bring all reagents into
complete solution prior to
initiating the polyesterification reaction, although the polymerization of
slightly soluble
monomers such as desaminotyrosyl tyrosine ethyl ester and succinic acid will
yield higher
molecular weight polymers when the amount of solvent is increased. The
reaction mixture can
also be heated gently to aid in the partial dissolution of the reactants.
The polymer molecular weight significantly increases as the amount of coupling
reagent
used is increased. The degree of molecular weight increase only begins to
level off around four
molar equivalents of carbodiimide per mole of carboxylic acid group.
Increasing the amount of
coupling reagent beyond four equivalents of carbodiimide has no further
beneficial effect. While
quantities of carbodiimide greater than four equivalents are not detrimental
to the
polyesterification reaction, such quantities are not cost-effective and are
thus not favored for this
reason.
Carbodiimide-mediated direct polyesterification can be performed in the
presence of the
catalyst 4-(dimethylamino)pyridinium-p-toluene sulfonate (DPTS). DPTS is
prepared in
accordance with the procedure of Moore et al, 1990, Macromol., 23:65-70. The
amount of DPTS
is not critical because the material is a true catalyst that is regenerated.
The catalytically effective
quantity is generally between about 0.1 and about 2.0 molar equivalents per
mole of carboxylic
acid group, and preferably about 0.5 equivalents per mole of carboxylic acid
group.
The reaction proceeds at room temperature, or about 20-30 C. The reaction
mixture can
be heated slightly (<60 C) prior to carbodiimide addition to partially
solubilize less soluble
monomers. However, the polymerization reaction itself should be conducted
between 20 C and
C. Within this temperature range, the reaction can be continued, with
stirring, for at least 12
hours, and preferably for from one to four days. The polymer is recovered by
quenching the
30
reaction mixture in methanol, from which the polyesteramide usually
precipitates while the
27
CA 02841499 2014-01-27
residual reagents remain in solution. The precipitate may be separated by
mechanical separations
such as filtration and purified by solvent washing.
In a particular procedure, equimolar amounts of pure, dried tyrosine-derived
diphenol and
dicarboxylic acid are weighed and placed in a round-bottomed flask, pre-dried
at 130 C. A
suitable magnetic stir bar is placed into the flask. Then 0.4 equivalents of
DPTS are added. The
flask is fitted with a septum and flushed with nitrogen or argon to remove
traces of moisture from
the reaction mixture. Next, a quantity of HPLC grade methylene chloride is
added via a syringe
and the reaction mixture is stirred vigorously to suspend the reactants. The
amount of methylene
chloride used will depend upon the solubility of the diphenol, or the
dicarboxylic acid, or both
monomers. At this stage, the reaction mixture may be slightly heated to
partially dissolve the
monomers. While it is not essential that the monomers be completely dissolved,
the quantity of
solvent should be sufficient to dissolve the polymer as it forms and thus
slowly bring the
monomers into solution.
4.0 equivalents of diisopropylcarbodiimide are then added to the reaction
mixture via a
syringe. After about 10 minutes, the reaction mixture becomes clear, followed
by the formation of
a cloudy precipitate of diiospropylurea. After stirring between 20 C and 30 C
for one to four
days, the reaction is terminated by pouring the reaction mixture slowly and
with vigorous stirring
into ten volumes of IPA- methanol. The polymer precipitates while the residual
reagents remain
dissolved in methanol, resulting in the formation of the clear supernatant.
The polymeric product is retrieved by filtration and washed with large amounts
of IPA-
methanol to remove any impurities. If desired, the polymeric products can be
further purified by
dissolving in methylene chloride (10% or 20% w/w) and reprecipitating in IPA-
methanol. The
polymeric product is then dried to constant weight under high vacuum.
In order to make polyesteramides having free carboxylic acid groups in the
pendant
chains, it is not sufficient to simply use the above-described polymerization
processes and
include monomers having free carboxylic acid groups. This is because the free
carboxylic acid
groups would cross-react with the carbodiimide coupling reagents used in the
above-described
processes. Instead, the method described in U.S. Patent No. 6,120,491, can be
employed. In this
method, a polyesteramide is synthesized, e.g., by the processes described
above, with the
inclusion of a monomer having a protecting group on the pendant chain that can
be selectively
28
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removed after the polyesteramide is synthesized. This protecting group must be
capable of being
removed without significant degradation of the polymer backbone and without
removal of ester
groups from pendant chains at those positions where it is desired that free
carboxylic acid groups
not be present in the final polymer.
Another method uses benzyl esters as the protecting group. Thus, if it is
desired to have a
polyesteramide with a certain percentage of free carboxylic acid groups, then
one would produce
an intermediate step polyesteramide with that percentage of monomers having
benzyl esters in
their pendant chains. The benzyl esters are selectively removed by palladium-
catalyzed
hydrogenolysis in N,N-dimethylformamide (DMF) or similar solvents such as N,N-
dimethylacetamide (DMA) and N-methylpyrrolidone (NMP) to form pendent
carboxylic acid
groups. Pure DMF, DMA, or NMP is necessary as the reaction solvent. The
reaction medium
must be anhydrous and the solvents have to be dried to ensure complete removal
of all benzyl
ester groups in the hydrogenolysis reaction. Essentially any palladium-based
hydrogenolysis
catalyst is suitable, and in certain methods, the palladium catalyst is
palladium on barium sulfate.
A level of palladium on barium sulfate between about 5% and about 10% by
weight is used in
certain embodiments. Certain methods also use 1 ,4-cyclohexadiene, a transfer
hydrogenolysis
reagent, in combination with hydrogen gas as a hydrogen source. The polymer
starting material
having pendent benzyl carboxylate groups can be dissolved in dimethylformamide
at a solution
concentration (w/v %) between about 5% and about 50%, or between about 10% and
about 20%.
For further details, see U.S. Patent No. 6, 120,491.
The co-polymers of tyrosine-based polyesteramides and poly(alkylene oxides)
depicted
in Formula 8 can be prepared by methods described in U.S. Patent Nos.
6,048,521 and 6,120,491.
A method of synthesizing strictly alternating (ab)n polymers by synthesizing a
trimeric
diol and condensing that diol with a diacid to produce the desired polymers is
shown below. The
first step is done under conditions that favor amide bond formation over ester
bond formation, for
example by using a mild coupling agent. Hence, the monomers are reacted to
produce the trimer:
HO-AP-NH2 + HO-C(0)-R2a-C(0)-0H HO-AP-NH-C(0)-R2a-C(0)-NH-AP-OH.
The trimer can also be represented by the structure shown below:
29
CA 02841499 2014-01-27
0 0
if
HO R¨CH¨WH¨C¨R2-C¨NHCH¨R OH
1
COORi COORi
The trimer is purified and reacted with a second diacid, HO-C(0)-R2b-C(0)0H,
using a
stronger coupling reagent to yield the strictly alternating repeat unit shown
below:
[0-AP-NH-C(0)-R2a-C(0)-NH-AP-O-C(0)-R2b-C(0)]
Another method also produces strictly alternating polymers (ab)n polymers by
first
synthesizing a trimer with protected amines. This is accomplished by coupling
an amine-
protected aminophenol with a diacid, isolating the resultant trimer with
protected amines at each
end, deprotecting the amines and reacting with a second diol under
condensation conditions. For
example, HO-AP-NHPr and HO-C(0)-R2a-C(0)0H are coupled to make PrHN-AP-O-C(0)
R2a-C(0)-0-AP-NHPr, where Pr is a protecting group that can be removed in the
presence of the
ester bonds in the trimer and AP is a shorthand for the remainder of the
aminophenol structure
other than the hydroxyl and amine groups. After deprotection, a second diacid,
HO-C(0)-R2b-
C(0)0H, is used to polymerize this trimer to form the strictly alternating
(ab)n polymers.
Another method produces strictly alternating (a)n polymers by reacting the
aminophenol
with an anhydride to produce a dimer with free OH and free COOH groups as
drawn in the
exemplary reaction scheme below:
HO-AP-NH2 + R2C(0)-0-C(0)-R2 -4 HO-AP-NH-C(0)-R2-COOH.
The reaction product is purified, more coupling reagent added to allow self
condensation
to proceed and produce a polymer with in which the diacid has an amide bond on
one side and an
ester bond on the other side as shown schematically below:
CA 02841499 2014-01-27
-(-0-AP-NH-C(0)-R2-C(0)-)(-0-AP-NH-C(0)-R2-C(0)-)(-0-AP-NH-C(0)-R2-C(0)+.
Another synthesis method produces a random copolymer of the aminophenol and
the
diacid. In this method, equimolar amounts of each compound are reacted in the
presence of a
coupling reagent, and catalyst as described, for example, in U.S. Patent Nos.
5,216,115;
5,317,077; 5,587,507; 5,670,602; 6,120,491; RE37,160E; and RE37,795E as well
as in the
literature, other patents and patent applications. Those of skill in the art
can readily adapt these
procedures to synthesize the polymers of the present invention. These polymers
generally have
low to moderate molecular weights (30-60 kDa).
The polymers and synthetic intermediates can be purified by those of skill in
the art using
routine methods, including extraction, precipitation, filtering,
recrystallization and the like.
Examples of coupling agents for the methods described above include, but are
not limited
to, EDCI.HC1, DCC, DIPC in combination with DPTS, PPTS, DMAP. Suitable
solvents
include, but are not limited to methylene chloride, chloroform, 1 ,2-
dichloroethane, either neat or
in combination with lesser quantities of NMP or DMF.
In certain embodiments, the polyesteramides have weight-average molecular
weights
above about 40-50 kDa. In other embodiments, the weight-average molecular
weight range is
about 40 kDa to about 400 kDa; or about 25 kDa to about 150 kDa; or about 50-
100 kDa.
Molecular weights can be calculated from gel permeation chromatography (GPC)
relative to
polystyrene standards without further correction. The molecular weight of the
polyesteramide
polymer used in the present invention is a factor that the skilled artisan
will consider when
developing a polyesteramide/antimicrobial combination for a particular use. In
general, keeping
all other factors constant, the higher the molecular weight of the polymer,
the slower will be the
release rate of the antimicrobial agent.
Systematic variations in polyesteramide properties can be obtained by varying
the nature
of the pendant group attached to the C-tenninus of the tyrosine-derived
diphenol and the
methylene groups in the dicarboxylic acid. One property that can be varied is
the glass transition
(Tg) temperature of the polyesteramide polymer. This is exemplified by the
approximately 1 C
increments in the glass transition temperature observed in the series of
polyesteramide polymers
31
CA 02841499 2014-01-27
described in Brocchini et al, 1997, J. Amer. Chem. Soc. 119:4553-4554. In
general, keeping all
other factors constant, the higher the Tg of the polymer, the slower will be
the release rate of the
antimicrobial agent. Therefore, one can vary the Tg of the polyesteramide
polymers, and thus the
release rate of the antimicrobial agent, by adjusting the identity of the
dicarboxylic acid and the
pendant chain ester groups.
The polydispersity index (PDI) of the polyesteramides should be in the range
of 1.5 to 4,
for example, 1.8 to 3. Manipulating the polydispersity provides another way to
adjust the release
rate of the antimicrobial agent. Higher molecular weight polymers release the
antimicrobial
agent more slowly than lower molecular weight polymers. Thus, a batch of a
particular polymer
with an average molecular weight of 80 kDa and a PDI of 1.5 should release the
antimicrobial
agent more slowly than another batch of the same polymer with an average
molecular of 80 kDa
but a PDI of 3, since the second batch is more polydisperse and thus has more
lower molecular
weight components than the first batch.
The tyrosine-derived diphenol monomers and corresponding tyrosine-derived
polyesteramides are biocompatible. The dicarboxylic acids generally are
naturally occurring
metabolites like adipic acid and succinic acid.
Since the polyesteramides contain an ester
linkage in the backbone, in certain embodiments, the polyesteramides are
biodegradable and the
degradation products, tyrosine, desaminotyrosine, and the dicarboxylic acids,
all have known
toxicity profiles.
Several members of the polyesteramides useful in the present invention were
extensively
tested in a variety of in vitro and in vivo assays and were found to exhibit
excellent
biocompatibility (Hooper et al., 1998, J. Biomed. Mat. Res. 41:443-454). In
long-term in vivo
studies, the present inventors have determined that the degradation products
of the
polyesteramides appear to be innocuous to surrounding tissue and promote
ingrowth. In
addition, surrounding tissue does not appear to exhibit inflammation in
response to the
polyesteramide degradation products. Implants in sheep, rabbits, dogs, and
rats have
demonstrated minimal tissue reaction and no local or systemic toxicity.
P22 Tyrosine-Derived Polyesteramides
The P22 family of tyrosine-derived polyesteramides is a subset of the tyrosine-
derived
polyesteramide family of polymers. The P22 family of polymers is synthesized
by polymerizing
32
CA 02841499 2014-01-27
a mixture of two phenolic monomers: desaminotyrosyl tyrosine ethyl ester (DTE)
and
desaminotyrosyl tyrosine (DT), protected as its benzyl ester, with succinic
acid. The P22 family
of polymers employs succinic acid; however, many different types of diacids
have been used in
the synthesis of tyrosine-derived polyesteramides. Varying the relative
concentration of DTE to
DT in the reaction mixture provides polymers with varied physicomechanical
properties but
identical degradation products. The molecular weights (MW) of the DTE and DT
monomers are
357.40 Da and 329.35 Da respectively. Below is provided the general structure
of the P22
Monomers (DTE: R = Ethyl; DT: R= Hydrogen):
0
airCH2¨C1-NH-CH-Cii2 11
Formula 12
The polymer designation is dictated by the percentage of DT content relative
to its
esterified counterpart (i.e. DT to DTE ratio). For instance, 22-10 contains
10% DT and
90% DTE). A higher proportion of DT results in a more relatively hydrophilic
polymer
with a higher glass transition temperature. The polymers can be synthesized
to molecular
weights ranging from 10 - 1301(Da. Below is provided the general structure of
the general
structure of the P22 polymers (R= -CH2-CH3 for DTE or -H for DT):
Ø640-4--1-64,6%, iy-L:picir0--0-1-citcgit)we
i-X
Formula 13
33
CA 02841499 2015-12-03
An exemplary P22 tyrosine derived polyesteramide has the structure P22-27.5
(27.5%DT
content; diacid = succinic acid).
Blends
The antimicrobial compositions of the invention also include blends of
polymers.
Accordingly, other polymers that can be blended with the tyrosine-derived
polyesteramides
described herein include, but are not limited to, polylactic acid,
polyglycolic acid and
copolymers and mixtures thereof such as poly(L-lactide) (PLLA), poly(D,L-
lactide) (PLA,
)polyglycolic acid [polyglycolide (PGA)], poly(L-lactide-co-D,L-lactide)
(PLLA/PLA), poly(L-
lactide-co-glycolide) (PLLA/PGA), poly(D, L-lactide-co-glycolide) (PLA/PGA),
poly(glycolide-
co-trimethylene carbonate) (PGA/PTMC), poly(D,L-lactide-co-caprolactone)
(PLA/PCL) and
poly(glycolide-co-caprolactone) (PGA/PCL); poly(oxa)esters, polyethylene oxide
(PEO),
polydioxanone (PDS), polypropylene fumarate, poly(ethyl glutamate-co-glutamic
acid),
poly(tert-butyloxy-carbonylmethyl glutamate), polycaprolactone (PCL),
polycaprolactone co-
butylacrylate, polyhydroxybutyrate (PHBT) and copolymers of
polyhydroxybutyrate,
poly(phosphazene), poly(phosphate ester), poly(amino acid), polydepsipeptides,
maleic
anhydride copolymers, polyiminocarbonates, poly[(97.5% dimethyl-trimethylene
carbonate)-co-
(2.5% trimethylene carbonate)], poly(orthoesters), other tyrosine-derived
polyesteramides, other
tyrosine-derived polycarbonates, other tyrosine-derived polyiminocarbonates,
other tyrosine-
derived polyphosphonates, polyethylene oxide,
polyalkylene oxides,
hydroxypropylmethylcellulose, polysaccharides such as hyaluronic acid,
chitosan and regenerate
cellulose, and proteins such as gelatin and collagen, and mixtures and
copolymers thereof,
among others as well as PEG derivatives or blends of any of the foregoing.
Commercially available polymers that can be blended with either the tyrosine-
derived
polesteramides or other polymers include Ostene , a commercially available,
water soluble
surgical implant material which is composed of water soluble ethylene oxide
and propylene
oxide copolymers.
Using polymer blends provides many advantages, including the ability to make
partially
resorbable devices and fully resorbable devices that have varied resorption
times for parts or all
of the device. For example, a partially resorbable device may increase
porosity over time and
thus permit tissue in growth. Those of skill in the art can readily pick
combinations of polymers
34
CA 02841499 2014-01-27
to blend and determine the amounts of each polymer need in the blend to
produce a particular
product or achieve a particular result.
Osteoinductive and Osteoconductive Agents
In certain embodiments, the antimicrobial compositions of the invention
further include
one or more osteoinductive agents. Osteoinduction refers to the stimulation of
bone formation.
Any material that can induce the formation of ectopic bone in the soft tissue
of an animal is
considered osteoinductive. For example, most osteoinductive materials induce
bone formation in
athymic rats when assayed according to the method of Edwards et al. (Clinical
Orthopeadics &
Rel. Res. 357: 219-228, 1998). Osteoinductivity in some instances is
considered to occur
through cellular recruitment and induction of the recruited cells to an
osteogenic phenotype.
Osteoinductivity may also be determined in tissue culture as the ability to
induce an osteogenic
phenotype in culture cells (primary, secondary, or explants). Any
osteoinductive agent known in
the art may be used. Non-limiting examples of osteoinductive agents include
bone
morphogenetic protein, insulin growth factor, transforming growth factor beta,
parathyroid
hormone, demineralized bone, and angiogenic factors.
The osteoinductivity of a compound can be evaluated based on an
osteoinductivity score
as determined according to the method of Edwards et al. (Clinical Orthopeadics
& Rel. Res. 357:
219-228, 1998). An osteoinductivity score refers to a score ranging from 0 to
4, in which a score
of "0" represents no new bone formation; "1" represents 1% to 25% of implant
involved in new
bone formation; "2" represents 26% to 50% of implant involved in new bone
formation; "3"
represents 51% to 75% of implant involved in new bone formation; and "4"
represents >75% of
implant involved in new bone formation. In most instances, the score is
assessed 28 days after
implantation. However, the osteoinductive score may be obtained at earlier
time points such as 7,
14, or 21 days following implantation.
In certain embodiments, the antimicrobial compositions of the invention
further include
one or more osteoconductive agents. Osteoconduction refers to the ability of a
material to serve
as a scaffold on which bone cells can attach, migrate, grow, and divide.
Osteoconductive agents
make it more likely for bone cells to fill the entire gap between two bone
ends. They also serve
as a spacer, which reduces the ability of tissue around the graft site from
growing into the site.
Any osteoconductive agent known in the art can be used. Non-limiting examples
of such
CA 02841499 2014-01-27
osteoconductive agents include human bone ("allograft bone"), purified
collagen, calcium
phosphate, hydroxyapatite, several calcium phosphate ceramics, and synthetic
polymers. Some
agents are reabsorbed by the body, while other agents may stay in the graft
site for many years.
Degradation
The compositions of the invention herein may be partially or completely
biodegradable.
A biodegradable polymer refers to a polymer that has hydrolytically or
oxidatively labile bonds
or that is susceptible to enzymatic action or other in vivo breakdown process,
or any combination
thereof, under physiological conditions, which action leads to the degradation
and/or breakdown,
whether partial or complete, of the polymer. Polymers that are biodegradable
have variable
resorption times that depend, for example, on the nature and size of the
breakdown products as
well as other factors.
A resorbable polymer refers to a polymer (1) with repeating backbone units
having at
least some bonds that are unstable under physiological conditions, i.e., in
the presence of water,
enzymes or other cellular processes, the polymer is biodegradable and (2) the
polymer as a whole
or its degradation products are capable of being taken up and/or assimilated
in vivo or under
physiological conditions by any mechanism (including by absorption,
solubilization, capillary
action, osmosis, chemical action, enzymatic action, cellular action,
dissolution, disintegration,
erosion and the like, or any combination of these processes) in a subject on a
physiologically-
relevant time scale consonant with the intended biological use of the polymer.
The time scale of resorption depends upon the intended use. The polymers of
the
invention can be manipulated to provide for rapid resorption under
physiological conditions, e.g.,
within a few days, to longer periods, such as weeks or months or years.
Medically-relevant time
periods depend upon the intended use and include, e.g., from 1-30 days, 30-180
days and from 1
to 24 months, as well as all time in between such as 5 days, 1, 2, 3, 4, 5 or
6 weeks, 2, 3, 4, 6 or
months and the like. Accordingly, the present invention includes
biocompatible, biodegradable
putties capable of resorption under physiological condition on medically-
relevant time scales,
based on appropriate choice of polymers. Breakdown of the polymers can be
assessed in a
variety of ways using in vitro or in vivo methods known in the art.
36
CA 02841499 2014-01-27
Binders
Compositions of the invention can include a binder. An exemplary binder is
polyethylene glycol (PEG; commercially available from Sigma-Aldrich, St.
Louis, MO). The
antimicrobial compositions can be formulated with any type of PEG, for
example, PEG-200,
PEG-300, PEG-400, PEG-600, PEG-1000, PEG-1450, PEG-3350, PEG-4000, PEG-6000,
PEG-
8000, PEG-20000, PEG-400-succinate, PEG-600-succinate, PEG-1000-succinate,
etc. In
particular embodiments, the percentage of PEG used in the antimicrobial
compositions of the
invention is about 1% to 99%, 5% to 95%, 10% to 80%, 15% to 75%, 30% to 70%,
20% to 50%,
or 25% to 40%. In particular embodiments, the percentage of PEG used in the
antimicrobial
compositions is about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%,
14%,
15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%,
30%,
35%, 40%, 45% 50%, 60%, 70% 80%, 90%, 95%, or 99%. Alternatively, the
antimicrobial
compositions can be formulated with a blend of different PEGs.
Other suitable binders include polypropylene glycols, and copolymers of
polyethylene
glycols and polypropylene glycols (e.g., block copolymers), for example those
available under
the trade name Pluronic available from BASF.
Additional binders include, but are not limited to: art-recognized suspending
agents,
viscosity-producing agents, gel-forming agents and emulsifying agents. Other
agents include
those used to suspend ingredients for topical, oral or parental
administration. Yet other
candidates are agents useful as tablet binders, disintegrants or emulsion
stabilizers. Still other
candidates are agents used in cosmetics, toiletries and food products.
Reference manuals such as
the USP XXII-NF XVII (The Nineteen Ninety U.S. Pharmacopeia and the National
Formulary
(1990)) categorize and describe such agents.
Exemplary binders include resorbable macromolecules from biological or
synthetic
sources including sodium alginate, hyaluronic acid, cellulose derivatives such
as alkylcelluloses
including methylcellulose, carboxy methylcellulose, carboxy methylcellulose
sodium, carboxy
methylcellulose calcium or other salts, hydroxy alkylcelluloses including
hydroxypropyl
methylcellulose, hydroxybutyl methylcellulose, hydroxyethyl methylcellulose,
hydroxyethyl
cellulose, alkylhydroxyalkyl celluloses including methylhydroxyethyl
cellulose, collagen,
peptides, mucin, chrondroitin sulfate and the like.
37
CA 02841499 2014-01-27
Carboxymethylcellulose (CMC) sodium is another example of a binder. CMC is
commercially available from suppliers such as, but not limited to: Hercules
Inc., Aqualon®
Division, Delaware; FMC Corporation, Pennsylvania; British Celanese, Ltd.,
United Kingdom;
and Henkel KGaA, United Kingdom. Carboxymethylcellulose sodium is the sodium
salt of a
polycarboxymethyl ether of cellulose with a typical molecular weight ranging
from 90,000-
700,000. Various grades of carboxymethylcellulose sodium are commercially
available which
have differing viscosities. Viscosities of various grades of
carboxymethylcellulose sodium are
reported in Handbook of Pharmaceutical Excipients (2nd Edition), American
Pharmaceutical
Association & Royal Pharmaceutical Society of Great Britain. For example, low
viscosity 50-
200 cP, medium viscosity 400-800 cP, high viscosity 1500-3000 cP.
Aside from binders that are flowable at room temperature, binders also include
reagents
such as gelatin, which are solubilized in warm or hot aqueous solutions, and
are transformed into
a non-flowable gel upon cooling. The gelatin composition is formulated so that
the composition
is flowable at temperatures above the body temperature of the mammal for
implant, but
transitions to relatively non-flowable gel at or slightly above such body
temperature.
In one embodiment, the binder of this invention is selected from a class of
high molecular
weight hydrogels including sodium hyaluronate (about 500-3000 kDa), chitosan
(about 100-300
kDa), poloxamer (about 7-18 kD), and glycosaminoglycan (about 2000-3000 kDa).
In certain
embodiments, the glycosaminoglycan is N,0-carboxymethylchitosan glucosamine.
Hydrogels
are cross-linked hydrophilic polymers in the form of a gel which have a three-
dimensional
network. Hydrogel matrices can carry a net positive or net negative charge, or
may be neutral. A
typical net negative charged matrix is alginate. Hydrogels carrying a net
positive charge may be
typified by extracellular matrix components such as collagen and laminin.
Examples of
commercially available extracellular matrix components include Matrigel.TM.
(Dulbecco's
modified eagle's medium with 50 µg/m1 gentamicin) and Vitrogen.TM. (a
sterile solution of
purified, pepsin-solubilized bovine dermal collagen dissolved in 0.012 N HCL).
An example of a
net neutral hydrogel is highly crosslinked polyethylene oxide, or
polyvinyalcohol.
Pharmaceutical Formulations
As formulated with an appropriate pharmaceutically acceptable carrier in a
desired
dosage, the antimicrobial compositions herein can be administered to humans
and other
38
CA 02841499 2014-01-27
mammals topically. Non-limiting examples of dosage forms for topical
administration of the
antimicrobial compositions of the invention include putties, ointments,
pastes, creams, lotions,
foams, or gels. The active agent is admixed under sterile conditions with a
pharmaceutically
acceptable carrier and any needed preservatives or buffers as may be required.
Preparations of
such topical formulations are well described in the art of pharmaceutical
formulations as
exemplified, for example, by Remington's Pharmaceutical Sciences.
In certain embodiments, the antimicrobial composition is a putty. The putty is
moldable,
spreadable, stretchable, and biocompatible. To form the putty the following
steps are performed:
dry blend the components (i.e., at least one antimicrobial agent, an optional
binder, and tyrosine-
derived polyesteramide); and mix all components until the desired putty- like
consistency is
achieved.
In other embodiments, the antimicrobial composition is formulated as an
ointment, a
paste, a cream, or a gel.
Ointments, pastes, creams, or gels may include the customary
excipients, for example animal and vegetable fats, waxes, paraffins, starch,
tragacanth, cellulose
derivatives, silicones, bentonites, silica, talc, zinc oxide, or mixtures of
these substances. The
carrier or excipient thereof provides a base for the ointments, pastes, creams
and gels. The
antimicrobial compositions of the invention are added to the base, and the
base and the
antimicrobial compositions are kneaded together to generate the ointment,
paste, cream, and gel
formulations.
In certain embodiments, the compositions are formulated such that the
antimicrobial
agent is covalently bound to the polymer, e.g., a tyrosine-derived
polyesteramide. In other
embodiments, the composition is formulated such that the antimicrobial agent
and the polymer,
e.g., a tyrosine-derived polyesteramide, are combined in a non-covalent
manner.
Uses
It has been found that the compositions of the invention are useful for
preventing
development of mediastinitis. In particular, the compositions of the invention
can be formulated
as a putty, paste, ointment/cream, gel, or foam and topically applied to an
esophageal perforation
in a subject or an incision site in a subject after the subject has undergone
a median stemotomy,
to prevent development of mediastinitis. The compositions of the present
invention provide one
or more of the antimicrobial agents described herein (e.g., rifampin and
minocycline) in
39
CA 02841499 2014-01-27
sufficient amounts to inhibit bacterial growth in the perforation or incision
site, thereby
preventing the development of mediastinitis (e.g., significantly reducing the
incidence of
mediastinitis in patients having an esophageal perforation, or in patients who
have undergone
median sternotomy).
Coronary artery bypass surgery (CABG) is one of the most common surgical
procedures
performed in the United States. Sternal wound infection (SWI) and
mediastinitis are devastating
complications associated with the prerequisite median sternotomy.
Mediastinitis is an infection
that results in swelling and irritation (inflammation) of the area between the
lungs, i.e., the
mediastinum. This area contains the heart, large blood vessels, windpipe
(trachea), esophagus,
thymus gland, lymph nodes, and connective tissues. Mediastinitis is a life-
threatening condition
with an extremely high mortality rate if recognized late or treated
improperly.
Sternotomy wounds become infected in about 0.5% to about 9% of open-heart
procedures and have an associated mortality rate of about 8% to about 15%
despite flap closure.
The rate of deep sternal wound infection (bone and mediastinitis) associated
with median
sternotomy ranges from between about 0.5% to about 5% and the associated
mortality rate is as
high as 22% independent of the type of surgery performed (Hollenbeak et al.,
Chest, 118:397-
402, 2000). Infection of the sternum is most commonly attributed to
contamination of the wound
bed at the time of surgery or during the acute healing phase when the wound is
still susceptible to
bacteria (Hollenbeak et al. Infection Control and Hospital Epidemiology,
23(4): 177, 2004; and
Yokoe et al., Emerging Infectious Diseases, 10(11):1924-1930, 2004).
After the CABG or other surgery has been completed, the sternum is usually
closed with
the assistance of wires or metal tapes. The sternal bony edges and gaps are
subsequently covered
and filled with a haemostatic agent. The most commonly used haemostatic agent
is bone wax
(bee's wax), despite the fact that bone wax has been reported to enhance
infection, cause a
foreign body reaction and inhibit bone growth. A median stemotomy is
complicated by
mediastinitis in about 1% to 2% of cases. Mortality for patients infected with
mediastinitis after
a median sternotomy is approximately 50%.
An esophageal perforation is a hole in the esophagus, the tube through which
food passes
from the mouth to the stomach. An esophageal perforation allows the contents
of the esophagus
to pass into the mediastinum, the surrounding area in the chest, and often
results in infection of
CA 02841499 2014-01-27
the mediastinum, i.e., mediastinitis. An esophageal perforation commonly
results from injury
during placement of a naso-gastric tube or a medical procedure such as
esophagoscopy or
endoscopy.
The esophagus may also become perforated as the result of a tumor, gastric
reflux with
ulceration, violent vomiting, or swallowing a foreign object or caustic
chemicals. Less common
causes include injuries that hit the esophagus area (blunt trauma) and injury
to the esophagus
during an operation on another organ near the esophagus. Rare cases have also
been associated
with childbirth, defecation, seizures, heavy lifting, and forceful swallowing.
For patients with an early diagnosis and a surgery accomplished within 24
hours, the
survival rate is 90%. However, this rate drops to about 50% when treatment is
delayed.
Other causes of mediastinitis include perforations of the esophagus or from
the
contiguous spread of odontogenic or retropharyngeal infections. However, in
modern practice, as
discussed above, most cases of acute mediastinitis result from complications
of cardiovascular or
endoscopic surgical procedures. The compositions of the present invention are
also useful for
preventing or reducing the rate of mediastinitis caused by perforations in the
esophagus or the
spread of infections is described herein.
The compositions of the present invention are also useful as a replacement for
haemostatic agents and bone wax, e.g. for covering bony edges and gaps after
surgery.
41
CA 02841499 2014-01-27
Equivalents
Various modifications of the invention and many further embodiments thereof,
in
addition to those shown and described herein, will become apparent to those
skilled in the art
from the full contents of this document, including references to the
scientific and patent literature
cited herein. The subject matter herein contains important information,
exemplification and
guidance that can be adapted to the practice of this invention in its various
embodiments and
equivalents thereof.
EXAMPLES
Example 1: Preparation of Polymer-Drug Powder
Tyrosine polyesteramide (P22-27.5) powder containing rifampin (10%) and
minocycline
(10%) drug was prepared by grinding polymer film. The polymer film containing
rifampin and
minocycline was prepared by solvent-cast method. Briefly, 8 g of tyrosine
polyesteramide P22-
27.5 was dissolved in 36 ml of THF. In a separate vial 1 g of rifampin and 1 g
of minocycline
was dissolved in 4 ml of methanol. The two solutions were mixed and poured
into a TEFLON
dish (10 cm diameter x 1.9 cm depth). The solution was left at room
temperature in a hood for
16-18 h to evaporate solvent. The dish was placed at 50 C oven under vacuum
for 24h. The
formulation bubbled up and formed a film. The film was crushed into the powder
using a small
mixer. The yield was 8.7 g Tyrosine polyesteramide polymer powder containing
10 % each of
rifampin and minocycline having MW range from 6 kDa to 70 000 kDa was prepared
by this
method. The MW weight of the polymer powder was assessed by GPC using against
PEG
standards.
Example 2: Preparation of PEG-Polymer Formulation
Various formulations were prepared in which P22-27.5-drug powder was combined
with
different ratios of PEG (MW 400) to yield various polymer-drug powder
combinations. Table 2
below shows different combinations.
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CA 02841499 2014-01-27
Table 2: P22-27.5- rifampin-minocycline formulations with PEG 400
# P22-27.5-drug PEJO 400, g % powder in
powder, g PEG 400
1 03 5.7 5
-It
2 0.3 2.7 10
3
0.3 1.7 ______ 15
4 0.3 1.0 23
=5
6.25
Example 3: Viscosity Measurements
Viscosity of oil-like (lubricant type) formulation was measured on Brookfield
viscometer
(Model DV II + Pro, Brookfield Engineering Lab Inc., Middleboro, MA) equipped
with
temperature probe and 4 various spindles. The formulation # 5 mentioned in
Table 2 was taken
into 20 ml scintillation vial and the viscosity was measured using spindle #
63 at ambient
conditions with a shear rate of 10 rpm. The viscosity of the formulation was
2230 - 2260 cp
(centipoise).
Example 4: Putty like formulation
A putty like formulation was prepared by increasing the amount of P22-27.5-
drug
polymer in PEG 400. Such formulation has more percentage of tyrosine
polyesteramide-drug
powder (P227.5-rifampin and minocycline) and less of PEG 400. 1 g of
tyrosine
polyesteramides-drug powder and 0.375 g of PEG 400 was found to form a
suitable putty. In
this putty like formulation, the PEG 400 percentage was 27.3 % and the
remaining percentage of
the formulation was tyrosine polyesteramide-drug polymer.
The putty like formulation had a dough like nature. The putty, when handled
with gloved
finger (dry, non-powdered latex gloves), did not indicate fiber formation
between surface of the
putty (dough) and the glove as finger left the surface. The putty was observed
to be malleable and
hand moldable at ambient conditions.
Example 5: Preparation of Polyarylate and Ostene Formulations
Ostene formulations containing tyrosine polyarylate (P22-27.5) polymer and
rifampin
(10%) and minocycline.HC1 (10%) drugs were prepared by the solvent-casting
method. Briefly,
Ostenee(CEREMED Inc., Lot # W2260408) and P22-27.5 were weighed into amber
color 100
43
CA 02841499 2014-01-27
mL screw cap jars and dissolved in 18 mL of tetrahydrofuran (THF). To
facilitate the dissolution
the containers were placed in 37 C incubator for ¨ 2h. In a separate 20 mL
amber vial rifampin
and minocycline-HC1 were weighed out and dissolved in 2 mL of methanol. The
two solutions
were mixed and poured into Teflon dishes (10 cm diameter x 1.9 cm depth) and
left at room
temperature in hood for ¨18 h to evaporate the solvent. The formulations were
then dried at 60 C
under vacuum for 48 h. The weights of Ostene , P22-27.5 polymer, and drugs
used for
preparing formulations are presented in Table 3. The yield was 2.3 g. It was
observed that the
original hand-molding nature of the Ostene is maintained even after inclusion
of tyrosine
polyarylate polymer and drug. This is important to the hemostatic function of
antibiotic bone
1 0 wax products.
Table 3: Details of the component weights used for making Ostene
formulations.
Sample Ostene P22-27.6 Rif-am* Minneyellnala
SO Polymer (g) (g)
OS 1.99945 one 0/4963 0,25033
OS-1 OTP6 1,80443 0,19686 0.25047 0.25045
0S-20TP6 1.59365 0.40543 0.25027 0/4995
Example 6: Characterization of Polyarylate and Ostene Formulations
GPC-MW
The MW of the Ostene formulations was assessed by gel permeation
chromatography
(GPC) against PEG standards. The sample was dissolved in N.N-dimethyl
formamide (DMF)
(containing 0.1% TFA) at a concentration of 10-12 mg/mL. The MW data is
presented in Table 4.
MW data of individual virgin samples is presented in Table 5. GPC
chromatograms of
the formulations (Table 4) showed multiple peaks. With addition of P22-27.5
polymer,
polydispersity index (PDI) increased noticeably. The large PDI is due to the
mixing of low and
high MW polymers.
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CA 02841499 2014-01-27
Table 4: GPC MW Data for Ostene - P22-27.5 Formulations.
SampsvMn POI
GPC showed multiple
OS ' 14297 4836 2.96
peaks
GPC showed multiple
0S-10T1'6 22107 5173 4.27
Peaks
GPC showed multiple
OS-20TP6 29711 5693 5.22
Peaks
Table 5: GPC MW Data for Ostene and P22-27.5 Polymer.
Polymer Mw /via PD1
GPC showed Two
Osten . 20275 9296 2.18
major peaks
?Poly 6 CPC showed Single
111984 33234 3.37
W22-27.5) Peak
¨
Thermal - Differential Scanning Calorimeter (DSC)
The Ostene formulations were also characterized by Differential Scanning
Calorimeter
(DSC) to check glass transition (Tg) temperature. Four (4) - six (6) mg of
sample was subjected to
a programmed two heating cycle method. Sample was heated from -50 C to 200 C
at a rate of
C/minute. The Tg temperatures were recorded in the 2nd heating cycle. All
formulations
10 showed a prominent melting transition around 50 C. This is typical of
PEG polymer transition.
Example 6: Drug release from the Ostene formulations
Actual loading of rifampin and minocycline in Ostene formulations
The drug content (loading) in each formulation was determined as per ATM 0421.
A
calibration plot was constructed for rifampin, minocycline by injecting
standard solutions of
known concentrations. A small portion of each formulation (approximately 20 -
35 mg) was
dissolved in 5 ml of DMSO and, 50 ml of methanol was added. The solutions were
mixed on a
vortex and injected. The drug loading was determined as an average of three
replicates (n=3).
CA 02841499 2014-01-27
The data is presented in Table 6. The actual rifampin loading was close 10 %.
Minocycline
loading was 7.5 %.
Table 6: Rifampin and minocycline estimation in the Ostene formulations (n=3)
- I Rif. rnW mg of Mitto mg' mg 01
Formulation formulation tonrwiation
0.073 I
OS 0.0965 0.059
-0.0963 0.0728
Average OLJ5
0.001.1 0.0017
0.0892 0.072-1
os-surp6 0.0970 0.0766
0.0999 = 0.0798
Averne 0.0934 ao763
0.0056 0.0037
0.0848 0.66SO
0S-20TP6 9/.0917 0.0676
0.0949 0.0725
Average O.0905 aO694
SI 0.0051 0.0027
Rifampin and minocycline release from Ostene formulations
The release was studied as per ATM 0427. Briefly, known quantities of each
formulation
were weighed into 60 ml amber screw cap bottle. Twenty (20) ml of freshly
prepared phosphate
buffer saline (PBS 0.1 M, pH 7.4) was added and the bottles were placed in 37
C incubator. The
sample was withdrawn and assayed by HPLC at 2, 4, 8 and 24 h time points. At
each time, the
entire PBS solution was replenished with fresh 20 ml PBS solution. The drug
release from
Ostene , OS-10TP6 and OS-20TP6 matrices are presented in Figures 1 and 2 for
minocycline
and rifampin respectively. Each time points represents an average of three
samples (n=3).
46
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Rifampin and minocycline release curves are presented in a single plot in
Figure 3. The release
kinetics are strongly influenced by the inclusion of P22-27.5 tyrosine
polyarylate polymer. About
75 % of minocycline was released from OS-10TP6 matrix in first 2h. This system
has 10%
(w/w) of P22-27.5 tyrosine polyarylate polymer. With the inclusion of 20 % of
P22-27.5 tyrosine
polyarylate polymer only 51 % of minocycline release was observed in first 2
h. At the end of
24 h, 86 % and 73 % of minocycline was released from OS-10TP6 and OS-20TP6
respectively.
Higher percentage of P22-27.5 in the ()steno? matrix slows down the release of
minocycline. A
similar trend was observed in rifampin release. The amount of rifampin
released however, was
less than minocycline at corresponding time point. At 2 h time point the
amount of rifampin
released was 53 and 24% from OS-10TP6 and OS-20TP6 respectively. The rifampin
release at
24 h was 73 % and 56% for OS-10TP6 and OS-20TP6 respectively. Rifampin and
minocycline
release from Ostene formulations was compared with AIG1S devices presented
in Figure 4
(AIGIS , available from TYRX, is an antibacterial envelope comprising a
knitted polypropylene
mesh substrate coated with a polyarylate resorbable polymer, containing
rifampin and
minocycline). The release profile shown by Ostene -P22-27.5 systems is almost
similar to that
of AIGIS .
Ostene itself is a highly hydrophilic water soluble polymer. As a result,
100% of
rifampin and minocycline were released from the Ostene matrix (Figures 1 & 2)
within the first
2 h. (Visual inspection indicates dissolution of Ostene matrix. The HPLC
indicates rifampin &
minocycline peak area that is probably outside the linear range of calibration
curve). Tyrosine
polyarylate polymer P22-27.5 is a hydrophobic material. The release is mainly
occurred by the
diffusion mechanism. The inclusion of hydrophobic material in the hydrophilic
Ostene matrix
slows down the water (buffer) uptake and therefore the rifampin and
minocycline drug release.
47
