STABILIZED COMPOSITIONS CONTAINING A PROSTAGLANDIN E

SUBSTANCES STABLES CONTENANT DE LA PROSTAGLANDINE E

English Abstract

ABSTRACT
A solution containing one or more prostaglandins E,
useful for therapeutic purposes, is stabilized by using
as the solvent an alkylene glycol or a monoester thereof.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A pharmaceutical composition having improved
stability comprising a solution of a prostaglandin E in an
alkylene glycol or a monoester.
2. A composition according to Claim 1, wherein said
prostaglandin E is a compound of formula (IV):
<IMG> (IV)
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a
hydrogen atom or a lower alkyl group; and R3 and R4 are the same
or different and each represents a lower alkyl group.
3. A composition according to Claim 1, wherein said
prostaglandin E is a compound of formula (V):
<IMG> (V)
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a hydrogen
atom or a lower alkyl group; and R3 and R4 are the same or
different and each represents a lower alkyl group.
4. A composition according to Claim 1, wherein said
prostaglandin is 9-oxo-11.alpha.,15.alpha.-dihydroxy-20-isopropylideneprost-
5(cis), 13(trans)-dienoic acid.
5. A composition as claimed in any one of Claims 1,
2 and 3, wherein said alkylene glycol or monoester thereof is
ethylene glycol, diethylene glycol, triethylene glycol, propylene
glycol, dipropylene glycol, 1,3-butanediol, 2,3-butanediol, 2,4-
18

pentanediol, hexylene glycol, 2,5-hexanediol, 2,4-heptanediol,
ethylene glycol monoacetate, propylene glycol monoacetate, poly-
ethylene glycol 200, 300, 400, 600, 1000, 2000, 4000 or 6000 or
polypropylene glycol 200, 300, 400, 750, 1200, 2000 or 4000.
6. A composition as claimed in any one of Claims 1, 2,
and 3, wherein the alkylene glycol is propylene glycol, polyethyl-
ene glycol 200, polyethylene glycol 300 or polyethylene glycol
400.
7. A composition as claimed in Claim 1, wherein said
prostaglandin E is 9-oxo-11.alpha.,15.alpha.-dihydroxy-20-isopropylideneprost-
5(cis),13(trans)-dienoic acid and said alkylene glycol is
propylene glycol, polyethylene glycol 200, polyethylene glycol
300 or polyethylene glycol 400.
8. A composition as claimed in any one of Claims 1, 2
or 3, wherein said solution is liquid.
9. A composition as claimed in any one of Claims 1, 2
or 3, wherein said solution is solid.
10. A process for preparing a stabilized prostaglandin
E composition, which comprises forming a solution of said
prostaglandin E in an alkylene glycol or monoester thereof.
11. A process according to Claim 10, wherein said
prostaglandin E is a compound of formula (IV)
<IMG> (IV)
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a hydrogen
atom or a lower alkyl group; and R3 and R4 are the same or different
and each represents a lower alkyl group.
12. A process according to Claim 10, wherein said
prostaglandin E is a compound of formula (V):
19

<IMG> (V)
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a hydrogen
atom or a lower alkyl group; and R3 and R4 are the same or
different and each represents a lower alkyl group.
13. A process according to Claim 10, wherein said
prostaglandin is 9-oxo-11.alpha.,15.alpha.-dihydroxy-20-isopropylideneprost-
5(cis), 13(trans)-dienoic acid.
14. A process as claimed in any one of Claims 10, 11
and 12, wherein said alkylene glycol or monoester thereof is
ethylene glycol, diethylene glycol, triethylene glycol, propylene
glycol, dipropylene glycol, 1,3-butanediol, 2,3-butanediol, 2,4-
pentanediol, hexylene glycol, 2,5-hexanediol, 2,4-heptanediol
ethylene glycol monoacetate, propylene glycol monoacetate,
polyethylene glycol 200, 300, 400, 600, 1000, 2000, 4000 or 6000
or polypropylene glycol 200, 300, 400, 750, 1200, 2000 or 4000.
15. A process as claimed in any one of Claims 10, 11
and 12, wherein the alkylene glycol is propylene glycol, poly-
ethylene glycol 200, polyethylene glycol 300 or polyethylene
glycol 400.
16. A process as claimed in any one of Claims 10, 11
and 12, wherein said alkylene glycol or monoester thereof is
liquid at normal temperatures and the solution is formed by
dissolving said prostaglandin E in said alkylene glycol or said
monoester.
17. A process as claimed in any one of Claims 10, 11
and 12, wherein said alkylene glycol or monoester thereof is
solid at normal temperatures and the solution is formed by

preparing an aqueous solution containing said prostaglandin E
and said alkylene glycol or said monoester and freeze-drying
the aqueous solution.
18. A process as claimed in any one of Claims 10, 11
and 12, wherein said alkylene glycol or monoester thereof is solid
at normal temperatures and the solution is formed by dissolving
said prostaglandin E in an aqueous solution of said alkylene
glycol or said monoester and freeze-drying the aqueous solution.
19. A process for preparing a stabilized prostaglandin
E composition wherein a solid alkylene glycol or a solid monoester
of an alkylene glycol is melted, a prostaglandin E is dissolved
in the melt, and the resulting solution is cooled.
20. A process according to Claim 19, wherein said
prostaglandin E is a compound of formula (IV)
<IMG> (IV)
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a
hydrogen atom or a lower alkyl group; and R3 and R4 are the same
or different and each represents a lower alkyl group.
21. A process according to Claim 19, wherein said
prostaglandin E is a compound of formula (V):
(V)
<IMG>
wherein: A represents an ethylene group or a cis-vinylene group;
R1 and R2 are the same or different and each represents a
hydrogen atom or a lower alkyl group; and R3 and R4 are the same
or different and each represents a lower alkyl group.
21

22. A process according to Claim 19, wherein said
prostaglandin is 9-oxo-11.alpha.,15.alpha.-dihydroxy-20-isopropylideneprost-
5(cis), 13(trans)-dienoic acid.
23. A process as claimed in any one of Claims 19,
20 or 21, wherein said alkylene glycol or monoester thereof is
ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, dipropylene glycol, 1,3-butanediol, 2,3-
butanediol, 2,4-pentanediol, hexylene glycol, 2,5-hexanediol,
2,4-heptanediol, ethylene glycol monoacetate, propylene glycol
monoacetate, polyethylene glycol 200, 300, 400, 600, 1000, 2000,
4000 or 6000 or polypropylene glycol 200, 300, 400, 750, 1200,
2000 or 4000.
24. A process as claimed in any one of Claims 19,
20 or 21 wherein the alkylene glycol is polyethylene glycol
2000, 4000 or 6000.
25. A process as claimed in Claim 19, wherein the
alkylene glycol is polyethylene glycol 2000, 4000, or 6000 and
the prostaglandin E is 9-oxo-11.alpha.,15.alpha.-dihydroxy-20-isopropylidene-
prost-5(cis), 13 (trans)-dienoic acid.
22

Description

s~
The present invention relates to a stabili~ed solution
of one or more prostaglandins E.
The prostaglandins are a family of biologically potent
lipid acids. The prostaglandins are divided into the types E,
F, A, B, C and D based on ~unctions in the cyclopentane ring.
The present invention is concerned with the group of compounds
known as prostaglandins E (hereinafter abbreviated as "PGE").
The prostaglandins, even when employed in very small amounts,
are known to possess a wide range of pharmacological activity.
The E series of prostaglandins are known to exert both a
vasodilating action and a bronchodilating action. The 20-
isopropylidene derivative of prostaglandin E2 (PGE2) has been
found to have only a bronchodilating activity without any other
pharmacological activity and is thus ideally suited for medical
use, as described in Belgian Patent Specification No. 833,577.
~owever, this derivative, like other prostaglandins E, has a
problem of stability which has not yet been solved.
In general, it has been found that solutions of PGE
in most solvents lose a substantial proportion of their
--1--

1~3~3f. 9~3
pharmacological activity within a very short time, even at
relatively low temperatures. For example, it has been reported
that the activity of a physiological saline solution of PGEl or
PGE2 is reduced to 58-62% of its original value within 15 days
at 4C [Srivastava et al, Lipids, Volume 8, 592 (1973)]. It has
also been reported that an ethanolic solution of PGE is unstable
under the conditions in which it would normally be used and
thus not only has to be stored at a temperature from -15C to -20C
but also has to be used within six months or, at most, one year
of its preparation [J. Pharm. Pharmacol., Volume 23, 804 (1971);
and Am. J. Hosp. Pharm. Volume 30, 236 ~1973)].
A multitude of different types of solvent has been
proposed to overcome this stability problem. Examples of the
solvents proposed include: tertiary alcohols having from 4 to
10 carbon atoms, e.g. t-butanol, as described in Japanese
Patent Provisional Publication No. 145515/75; vegetable oils and
or acid esters, e.g. sesame oil, peanut oil, ethyl oleate or ethyl
carbonate, as described in Japanese Patent Provisional Publication
No. 105815/75; anhydrous but water-miscible non-protonic polar
organic
; ~ 30
-2-

SS
solvents, e.g. tetramethylurea, dimethyl sulphoxide, diisopropyl
ketone, acetone or dimethylacetamide, as described in Belgian
Patent Specification No. 790,840; and organic acid esters, e.g.
ethyl acetate, ethyl propionate or isopropyl myristate, as
described in Japanese Patent Provisional Publication No. 88054/75.
Elowever, most of these solvents are physiologically
unacceptable when administered directly to a living human body
and none has, as yet, been used in practice. Moreover, the
improvement in stability has not generally been of such a level
that PGE can be stored without difficulty.
We have now surprisingly discovered that a specific
class of solvents will dissolve the prostaglandins E and that
the resulting solutions will retain their pharmacological
activity for a considerable period of time, the improvement
in stability being far greater than that achievable with prior
art solvents. The class of solvents discovered by the present
invention are the alkylene glycols and their monoesters.
Thus, the present invention provides a pharma-
~0

ceutical composition comprising a PGE dissolved in an alkyleneglycol or a monoester thereof and also provides a method of
producing such a composition by forming a solution of the PGE
in the alkylene glycol or monoester.
Although we do not wish to be limited by any theory and
although, in any solution, interactions between solvent and solute
are generally so complex as to defy precise analysis, we believe
that the reason why the alkylene glycols and monoesters thereof
provide a stable solution of PGE is as follows:
It is known that prostaglandins E tend to convert
to the corresponding prostaglandin A by elimination of the hydroxy
group on the five-membered ring; this is caused by the electron-
attractive effect of the carbonyl group at the 9-position. The
resulting prostaglandin ~ then tends to isomerize to the
corresponding prostaglandin B. This process is illustrated by
the following reaction scheme, in which the compound of formula
(I) is PGE2 or a derivakive thereof, compound (II) is PGA2 or a
derivative thereof, compound (III) is PGB2 or a derivative thereof
and R represents a substituent.
. .

O
~'C~H " ~\~O~
~R ~\/
~1~ 0~
Il) 11~)
OOH
01
1~1) '
The nature of the solvent in which the PGE is
dissolved influences the hydroxy group elimination reaction;
protonic solvents tend to promote it. Thus, the ll-hydroxy
group (in the 5- membered ring) of a PGE is easily eliminated
in a protonic solvent; this is probably due to an intermolecular
hydrogen bond formed between the 9- carbonyl group and the
s.olvent. Accordingly, the elimination reaction is probably
promoted by solvents having a large proton donating capacity,
e.g. methanol or ethanol. It is believed that the alkylene
glycols and their monoesters have limited proton donating
capacity and, for this reason, do not promote the hydroxy

group elimination reaction and thus provide solutions of
improved stability.
Examples of prostaglandins E which can be stabilized
by the method of the present invention include PGEl, PGE2 and
derivatives thereof, including the corresponding ll-deoxy
derivatives. Of these compounds, the invention may most usefully
be applied to prostaglandins of general formula (IV):
O ' , ' .'
)4\A~\r~oQR2 q3
~ 1~ (IV)
nH Q~ Rl
[in which: A represents an ethylene group or a c -vinylene
group; Rl and R2 are the same or different and each represents
a hydrogen atom or a lower alkyl group, preferably having from
1 to 3 carbon atoms (e.g. methyl, ethyl, n-propyl or isopropyl);
and R3 and R4 are the same or different and each represents
a lower alkyl group, preferably having from 1 to 3 carbon atoms
(e.g. methyl, ethyl, n-propyl or isopropyl)] and the corresponding
ll-deoxy derivatives, which have the general formula (V):
O
~)~A--G~ R~ (V)
\~ R~
OU R1
--6--

(in which A, Rl, R , R and R4 are as defined above).
Examples of compounds of the above formulae are as
follows:
1. 9-Oxo-lla,15~(or~ dihydroxy-20-isopropylidene-
; prost-13(trans)-enoic acid and its methyl, ethyl,
n-propyl and isopropyl esters;
2. 9-Oxo-11~,15a(or~)-di.hydroxy-20-isopropylidene-
prost-5(cls), 13(trans)-dienoic acid and its methyl,
ethyl, n-propyl and isopropyl esters;
3. 9-Oxo-11~,15~(or~)-dihydroxy-17~-methyl-20-iso-
propylideneprost-13(trans)-enoic acid and its methyl
ethyl, n-propyl and isopropyl esters;
~ 4. 9-0~o-11~,15~(or~)-dihydroxy-17~-methyl-20-iso-
; propylideneprost-5(cis),13(trans)-dienoic acid and
its methyl, ethyl, n-propyl and isopropyl esters;
5. 9-Oxo-11~,15~(or~)-dihydroxy-17~-methyl-20-(1- -
methylisopropylidenelprost-13(trans)-enoic acid
and its methyl, ethyl, n-propyl and isopropyl esters;
3Q

s
6. 9-Oxo~ , 15~(or ~)-dihydroxy-17~-methyl-20-(1-
methylisopropylidene)prost-5(cis), 13(trans)-dienoic
acid and its methyl, ethyl, n-propyl and isopropyl
esters;
7. 9-Oxo-lla, 15a~or ~)-dihydroxy-17~-methyl-20-(1,3-
dimethylisopropylidene)prost-13(trans)-enoic acid
and its methyl, ethyl, n-propyl and isopropyl estersi
; '
8. 9-Oxo-lla, 15a(or ~)-dihydroxy-17~-methyl-20-(1,3-
dimethylisopropylidene)prost-5(cis), 13(trans)-dienoic
acid and its methyl, ethyl, n-propyl and isopropyl
esters;
9. 9-Oxo-lla,15a(or ~)-dihydroxy-20-(1-methylisopropyl-
idene)prost-13(transl-enoic acid and its methyl, ethyl,
n -propyl and isopropyl esters;
10. 9-oxo-Ila, 15a(or ~)-dihydroxy-20-(1-methylisopropyl-
idene)prost-5-(cis), 13(trans)-dienoic acid and its
.: methyl, ethyl, n-propyl and isopropyl esters;
.
. ~ 11. 9-Oxo-lla~15a(or ~)-dihydroxy-20-(1,3-dimethyliso-
propylidene)prost-13(trans)-enoic acid and its methyl,
--8--

ethyl, n-propyl and isopropyl esters;
12. 9-Oxo-lla, 15~(or ~)-dihydroxy-20-(1,3-dimethyl-
isopropylidene)prost~5(cls), 13(trans)-dienoic
acid and its methyl, ethyl, n-propyl and isopropyl
esters;
13~ 9-Oxo-15~(or ~)-hydroxy-20-isopropylideneprost-
13(trans)-enoic acid and its methyl, ethyl, n-
propyl and isopropyl esters;
14. 9-Oxo 15~(or ~)-hydroxy-17~-methyl-20-isopropyl-
ideneprost-13(trans)-enoic acid and its methyl,
ethyl, n-propyl and isopropyl esters;
15. 9-Oxo-15a(or ~)-hydroxy-20-isopropylideneprost-5-
(cis), 13(trans)-dienoic acid and its methyl,
ethyl, n-propyl and isopropyl esters; and
16. 9-Oxo-15~(or ~)-hydroxy~17~-methyl-20-isopropyl-
ideneprost-5-(cls), 13(trans)-dienoic acid and
its methyl, ethyl, n-propyl and isopropyl esters.
Of these compounds, we particularly prefer 9-oxo-
lla, 15~-dihydroxy-20-isopropylideneprost-5(cis), 13(trans)-dienoic

2~i~
acid, otherwise known as 20-isopropylidene-PGE2, which has the
formula (VI):
h ~ ~aH ~ (VI)
Q~ .
The solvent employed in the present-invention is an
alkylene glycol or monoester thereof. Examples of suitable
alkylene glycols include: ethylene glycol; diethylene glycol;
triethylene glycol; propylene glycol; dipropylene glycol; 1,3-
butanediol; 2,3-butanediol; 2,4-pentanediol; hexylene glycol;
2,5-hexanediol; 2,4-heptanediol; polyethylene glycols 200, 300,
400, 600, 1000, 2000, 4000 and 6000; and polypropylene glycols
200, 300, 400, 750, 1200, 2000 and 4000. The monoester employed
is preferably an ester of any of the above-mentioned alkylene
glycols with a lower aliphatic acid, for example ethylene glycol
~; monoacetate or propylene glycol monoacetate. It is also possible
to use block copolymers of the above - listed polyethylene
glycols and polypropylene glycols.
Any of these alkylene glycols and monoesters may be
employed by itself or a mixture of any two or more may be used.
--10--

s~
of the alkylene glycols and monoesters exemplified
above, we particularly prefer propylene glycol and polyethylene
glycols 200, 300 and 400; these compounds form solutions easily
and have good physiological tolerances.
Some of the alkylene glycols and monoesters thereof
which may be used in the present invention are liquids at normal
temperatures, whereas others are solids. Where the alkylene
glycol or monoester is a liquid at ordinary temperatures, the
solution of the present invention can easily be formed by dis-
solving ~he PGE in it in the same way as any other solid is
dissolved in a liquid which is a solvent for it. Where the
alkylene glycol or monoester thereof is solid at ordinary
temperatures, the preferred method of forming the solution is to
dissolve the PGE in an aqueous solution of the alkylene glycol
or monoester, or add water to a mixture of the PGE and the alkyl-
ene glycol or monoester, and then freeze-dry the resulting
aqueous solution., Alternatively, where the alkylene glycol or
monoester thereof is solid at normal temperatures, a solution
may be formed by heating the alkylene glycol or monoester to melt
it and then dissolving the PGE in the molten glycol. The resulting
solutlon is then cooled to storage temperature to form a solid
solution. The temperature at which the glycol or, monoester is
heated obviously depends on its melting point, but account should
also be taken of the temperature stability of the PGE. It is
preferred that the molten solution containing the PGE should be
at about the minimum tempera'ture necessary for melting and that
it should be ~ept at that temperature for the minimum necessary
time. This procedure is particularly useful with polyethylene
glycols 2000, 4000 and 6000 at the glycol solvent.
' There is no particular limitation upon the concentration
of the PGE in the solution, although the maximum concentration
will, of course, depend upon the solubility of the PGE in the
selected alkylene glycol or monoester. However,
-- 11 --

2ss
for practical and economic reasons, it is preferred that
sufficient PGE should be dissolved in the alkylene glycol
or monoester to give a final PGE concentration of from about
lOy to 1000~ per ml of the final composition, more preferably
about 100~/ml.
The invention is further illustrated by the following
non-limiting Examples. In these Examples, the residual activity
of the PGE in solution after ageing was determined by the
following biological test.
A sample of bronchial muscle excised from a guinea
pig was contracted with histamine. The bronchial muscle sample
was then kept at 36C and suspended in Tyrode solution aerated
with a gas mixture comprising 95% by volume 2 and 5% by volume
CO2, and its tension was measured. Histamine was added to the
- solution to a final concentration of 10 5 g/ml and, after contra-
ction of the excised muscle sample became constant, the desired
test sample was added to ,determine the concentration required for
50% relaxation. The residual activity is reported as a percentage
of the activity after ageing for 4 weeks at 40C to the
activity of an initial test sample.

` -
25~
EXAMPLES 1 to ll
-
lO0 mg of the prostaglandin E specified in Table 1
were charged into a l litre vessel and then sufficient of the
solvent indicated in Table 1 was added to make a total volume
of l litre. The activities of the resulting solutions were
measured both before and after keeping at 40~C for 4 weeks.
The results are summarized in Table lo
-13-

op
cn
~Q ~
o
~ o~ o
)
o o ;., o o
~ o ~ o ~ o ~ ~ o
~ O O a) o ~ ~ o
a~
~ ~ a~
,. o ~ ~ r~ 4
,. u~ O O a) ~ ~ p~
:~
~1
~1
~ : - ~
~ N C~
~ ~ u v ~
p~
~ a) a) a) a
c~
~ $
~J
:~
0~ Po OQ'0~ 0~ 0~ 0 0
51 h h h h h h h
~ P~ P~ ~ ~ P~P~
:. O o O O O O O O
U~
. ,. I o o o o I o o
.
zo
. ~ CO ~ O
X
.
--14--

2S~
,, (~
~ ~ J o
-
--15--

5~
It can be seen from the Table that solutions using
the alkylene glycol and monoester solvents of the present
invention are substantially more stable than those using the prior
art solvent, ethanol. The solvents of the present invention
also compare favourably with other prior art solvents. Fo~
example, Japanese Patent Provisional Publication No. 145515/75
describes the use of t-butanol as a solvent and this shows a
residual activity of 62 - 83% after 2 weeks at 50C; ageing for
2 weeks at 50C is substantially equivalent to agein~ for 4
weeks at 40C. Accordingly, it can be concluded that the
solvents of the present invention are substantially better than
t-butanol also.
E~AMæLE 12
:`
100 mg of 20-isopropylidene PGE2 were charged into a
1 litre vessel. 50 g of polyethylene glycol 6000 were added and
then distilled water was added to a total volume of 1 lit~e. The
resulting solution was divided into vials and then freeze-fried by
a conventional method. The preparation thus formed showed
,
-16-

~ 5~
a residual ac~ivity of 75~ after 4 weeks at 40PC.
On investigation of the freeze-dried solution, it was
found that it contained residual traces of water, indicating
that drying had not been complete. It was thoughtthat this
trace of water had partially destroyed prostaglandin activity
and resulted in the relatively low residual activity. Accordingly
the experiment was repeated taking great care to remove all water
during freeze-drying. This time the residual activity was 90
percent after 4 weeks at 40 degrees celsius. The importance
of complete drying is thus demonstrated.
EXAMPLE 13
One KG of polyethylene glycol 4000 was melted at 60
degrees celsius, and then 100 mg of 20 isopropylidene PGE2 were
dissolved in the melt. The resulting solution was cooled and
finely divided to form a powder. This powder has a residual
activity of 90 percent after 4 weeks at 40 degrees celsius.
-17-