Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR TAKING CRYSTAL~IaINE IRON DF.XTRAN
TP.e n'cal Field
The present invention relates to a process for making iron preparations useful
in the
s treatment of iron deficiencies. More particularly, the invention relates to
a process for the
preparation of crystalline iron(III)-dextran complex.
ack~round ~f th_P Tnvention
Iron dextran has been known for about 35 years. It has been utilized primarily
as an
1 o injectable agent for countering iron deficiencies in animals and human
patients, having severa
advantages over other iron preparations including low toxicity, low incidence
of adverse
reactions, and satisfactory rate of iron adsorption.
Iron dextran is typically prepared by forming a complex of dextran with
iron(III). The
dextrans used are generally either (i) partially depolymerized dextrans having
a molecular
i s weight in the range of 1,000 to 10,000 or (ii) modified forms of dextran
such as hydrogenated
dextrans or oxidized dextrans. The iron(TII) is prepared by neutralization of
an aqueous
solution of an iron(III) salt with an alkali. In order to prepare an aqueous
iron dextran solution
in a form suitable for injection, it is necessary to remove the soluble salts
formed in the reaction
between the water-soluble ferric salt and the dextran. This can be
accomplished by known
2o procedures such as dialysis or reverse osmosis, or by precipitation of the
iron dextran complex
from the aqueous solution, followed by drying and reconstitution with water.
Isolation of the iron-dextran complex from the aqueous solution by
precipitation with a
water-miscible solvent is known in the art. United States Patent No. 4,599,405
describes
centrifuging and filtering the aqueous iron-dextran solution, followed by
precipitation of the
2s complex with ethanol. The complex is then washed with ethanol, separated,
and dried to give
the iron-dextran complex as a solid which is then reconstituted with water to
form an inject;ible
solution.
United States Patent Number 3,093,545 describes isolation of a treacle-like
solid iron
dextran complex by addition of methanol to the aqueous iron dextran solution,
allowing thc~
3o solid to settle, and decanting the supernatant liquid. The residual solid
is then washed with
aqueous ethanol, the liquid is decanted, and the process repeated. The
residual liquid is
removed by vacuum filtration, and the remaining solid complex is dried.
United States Patent Number 3,574,184 describes isolation of a treacle-like
solid iron
dextran complex by addition of ethanol to the aqueous solution and one or more
centrifugation
35 Steps.
United States Patent Number 2,885,393 describes a process for making a
gelatinous
form of an iron dextxan complex wherein the complex is purified by
precipitation from aqueous
solution by addition of isopropanol, followed by decanting the supernatant
liquid, redissolving
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the solid in water, and repeating the process. After further processing, the
iron dextran
complex is obtained as an aqueous solution.
United States Re. 24,642 describes purification of the iron-dextran complex by
filtering
the aqueous solution, precipitating the complex by mixing with ethanol,
filtering the gelatinous
s solid., and redissolving the complex in water and repeating the
precipitation with ethanol. The ,
iron-dextran complex is then dissolved in water to form the injectable
solution.
All of the prior art methods for isolating the solid iron-dextran complex
require addition
of the precipitating solvent to the aqueous iron dextran solution and result
in gelatinous or
treacle-like solids which are difficult to filter. Alternate methods of
solvent removal, such as
1 o centrifugation or decantation are therefore required. Substantial further
processing of the initial
solid is also required to obtain complex of sufficient purity for use as
injecta.ble solutions.
Consequently, there remains a need for a method of precipitation which
produces pure iron
dextran complex which can be easily isolated by filtration and dried. The dry
powder can then
be stored and reconstituted as needed to form the aqueous solution, thereby
obviating storage
i s difficulties which result from the prior art methods in which the complex
is prepared and/or
stored as a 5-to-10°~o aqueous solution.
Summary of t_he Inv n ,nn
It has now been found that a process in which an iron-dextran complex is added
to a
2o solvent, instead of the solvent being added to the iron-dextran complex,
unexpectedly results in
the formation of an easily-filtered crystalline solid which can be dried to a
powder and easily
stored for later reconstitution with water. This ease of filtration, and the
elimination of the need
for reverse osmosis, decanting, or other means of isolation of the solid from
the residual
aqueous solution, offer a means of considerable cost savings.
2s Accordingly, in one aspect of the present invention is disclosed a method
of making
crystalline iron-dextran complex, comprising the steps of:
(a) combining an aqueous solution of dextran in which the dextran has an
average
molecular of 3,000 to 6,000 with an aqueous solution of an iron(III) salt;
(b) combining the mixture with alkali;
30 (c) heating and stirring the mixture until the formation of an iron-dextran
complex is
substantially complete;
(d) acidifying the mixture;
(e) precipitating the iron-dextran complex by adding the mixture to a water
miscible
solvent; and
ss (f) isolating the crystalline iron-dextran complex.
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3
In another aspect of the present invention is disclosed a process for the
crystallization of
an iron-dextran complex in readily-filterable form, comprising adding slowly,
with stirring, ;an
aqueous iron-dextran solution to a vessel already containing a water miscible
organic solvent..
In a further aspect of the present invention are disclosed crystalline iron-
dextran
complexes prepared by the above processes.
Detailed Description of the Invention
Dextran is a polysaccharide polymer of formula (C6H1p05)n composed exclusively
of a-
D-gluconpyranosyl units linked predominately a-1-6 and obtained by the action
of bacteria
1 o grown on a sucrose substrate by methods well-known in the art. Native
dextrans usually have
high molecular weigh>~ Lower molecular weight dextrans are prepared by partial
depolymerization of the native dextrans by methods known in the art, such as
treatment with
mineral acid.
A dextran obtained by partial depolymerization of such a native dextran may be
further
i s modified, as for example by partial reduction using sodium borohydride or
catalytic
hydrogenation, or by oxidation. The term "dextran" as used herein is intended
to include
dextran, reduced dextran, and oxidized dextran. Treatment of unmodified
dextran with mild
oxidizing agents such as sodium or potassium periodate introduces carboxyl
groups on the
terminal glucose unit. Optionally, the terminal glucose unit may be oxidized
to carboxylic
2o groups using, for example, bromine, sodium hypobromite, sodium bromite,
sodium
hypochlorite or sodium chlorite. In one embodiment of the invention, dextran
is dissolved in
water and oxidized by treatment with between about 0.4 and about 0.6 parts per
weight (ppv~r)
5°1o aqueous sodium hypochlorite, followed by between about 0.10 and
about 0.15 ppw of
aqueous sodium hydroxide. The oxidation is best earned out at ambient
temperature (about 15
2s to about 35 °C). A representative dextran contemplated for use in
the present invention is a
partially depolymerized dextran having a molecular weight of between about
1,000 and about
10,000, preferably between about 3,000 and about 6,000.
In accordance with the foregoing, between about 1 and about 10 ppw of such a
dextran
are dissolved in water (preferred dextrans being unoxidized or oxidized
dextrans and oxidized
3 o dextrans being most preferred). A particularly preferred embodiment of the
process of the
present invention utilizes between about 1.0 and about 1.5 ppw of oxidized
dextran having a.
molecular weight of 5,000 to 6,000. The aqueous dextran solution is then added
with stirring
to an aqueous solution of about 1 ppw of iron(I117, where the term "iron(III)"
means trivalent
hydrous ferric oxide. The iron(IZI) solution is prepared by neutralizing a
ferric salt with alkali.
ss Suitable ferric salts include any water-soluble salts which generate
hydrous fernc oxide when
treated with alkalis. Representative salts include fernc chloride, ferric
nitrate, ferric sulfate,
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ferric perchlorate, ferric acetate, fernc trichloroacetate, ferric citrate and
the like, as well as
double salts such as ferric ammonium sulfate or fernc ammonium citrate and the
like. Of the
above salts, ferric chloride is particularly preferred. Representative alkalis
include the
hyroxides and carbonates of sodium, lithium and potassium. The ferric salt may
be neutralized
by treatment with excess alkali, or may be formed in a two step process
involving partial
neutralization with alkali followed by addition of the dextran solution and
additional alkali to
achieve complete neutralization and complex formation. The iron( solution is
preferably
prepared by adding between about 0.14 and about 0.24 ppw of aqueous sodium
carbonate to an
aqueous solution containing about 1 ppw of hydrated fernc chloride.
t o After combining the aqueous iron(III) and dextran solutions, the mixture
is made basic
by addition of between about 0.15 and about 0.25 ppw alkali, preferably sodium
hydroxide.
The mixture is then heated, preferably at between about 80 and about 100
°C, and stirred until
complex formation is complete. When unoxidized dextran is used, gradual
heating may be
required to prevent formation of a heterogeneous mixture. The solution may
then be acidified
i s using solid, gaseous or liquid acid, preferably aqueous hydrochloric acid,
to obtain a pH of
between about 4 and about S. The solution may then be heated, preferably at
between about
118 and about 135 °C, at a pressure of between about 10 and about 20
psi (68 and 138 KPa).
After cooling to ambient temperature, crystalline iron-dextran complex is
obtained by adding the
reaction solution to a water-miscible organic solvent in a solution-to-solvent
ratio of about not
20 less than 1:l by volume, followed by filtration. Representative solvents
include methanol,
ethanol, isopropanol, acetone and the Like, with methanol being the most
preferred solvent and
(when methanol is used) the preferred ratio of aqueous iron-dextran solution
to solvent being
about 1:8. To reduce solvent volume, the aqueous iron-dextran solution may be
concentrated
prior to addition to the solvent. The initially obtained crystalline iron-
dextran may be washed
2s with additional solvent prior to drying and storage.
The process of the present invention will be better understood in connection
with the
following Examples, which are intended solely as an illustration thereof.
Example 1
30 ~paration of ('r~stalline Iron-Dextran Complex usin~Oxidized Dextran
To a solution of molecular weight 5000 Dextran (60.7 g) in water (I08 mL) was
added
bleach (32 mL) and S% aqueous sodium hydroxide (7.5 mL). The solution was
stirred for one
hour and then was refrigerated for 17 hours. To a stirred solution of ferric
chloride (60 g) in
s5 water (300 mL) was added, dropwise over 60 minutes, a solution of sodium
carbonate (11.8 g)
in water (100 mL), followed by the bleach-dextran solution. To the resulting
solution was
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added a solution of sodium hydroxide (22.6 g) in water (100 mL) over a 60
minute period. '7Che
mixture was heated at 90-100 °C for 90 minutes and then was cooled to
ambient temperature
and acidified with to pH 4 with HCl to give 907 g of iron-dextran solution. A
447 g aliquot
was removed and concentrated to a volume of 160 mL and then was added with
stirring to 1038
s g of methanol. The resulting crystalline solid was collected by filtration
and washed with
methanol. The solid was slurried in methanol (173 g), filtered, and dried to
afford 15.63 g of
iron-dextran powder. The material passed gel permeation chromatographic
analysis.
>?:enaration of Crystalline Iron Dextran Complex using Unoxidized Dextran
To a solution in water (70 mL) of fernc chloride (24.0 g) was added a solution
of
sodium carbonate (4.7 g) in water (40 mL) over an 80-minute period. To the
mixture was
added a solution of dextran (27.3 g) in water (70 mL), followed by addition,
over 40 minutes,
is of a solution of sodium hydroxide (9.0 g) in water (110 mL). The mixture
was then added t~o
methanol (350 mL). The resulting solid was filtered, dissolved in water (150
mL) and heated at
85 °C for 60 minutes. The mixture was cooled and added to methanol (
100 mL). The resulting
solid was filtered and dried to afford 19.4 g of iron dextran powder. The
material passed gel
permeation chromatographic analysis.
example 3
P~paration of Crystalline Iron Dextran Complex with fn Situ Oxidation of
Dextran
To a solution of molecular weight 5000 dextran (27.3 g) in water (70 mL) was
added
2s 2.25 N aqueous sodium hydroxide (5 mL); the resulting mixture was heated at
75-80 °C for 30
minutes_ The solution was cooled and added to a fernc solution prepared by
treating a solution
of ferric chloride (24.0 g) in water (70 mL) with 1.1 N aqueous sodium
carbonate (40 mL).
The resulting solution was heated to 80-90 °C, cooled, and added to
methanol (100 mL) witm
stirnng. The resulting crystalline solid was filtered and dried to give iron-
dextran powder. The
s o material passed gel permeation chromatographic analysis.
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Example 4
dal Preparation of Crystalline Iron-Dextran
To a 30-gallon reactor containing a 25 °C solution under NZ of ferric
chloride
s hexahydrate (5.0 kg) in degassed water (25 kg) was added a solution of
sodium carbonate (1.0
kg) in water (8.3 kg). The temperature was maintained at 20-26 °C while
stirring at 30-50 rpm
during the addition. In a 50-gallon reactor, dextran (5.2 kg) was dissolved in
water (9.1 kg).
To the dextran solution was added 5°k aqueous sodium hypochlorite (2.9
kg) and after
thorough mixing 10% aqueous sodium hydroxide solution (0.7 kg) was added. The
solution
i o was stirred until it did not react with KI starch paper. The oxidized
dextran solution was then
added to the ferric solution over 5 minutes while maintaining the temperature
of the ferric
solution at 23-25 °C and stirnng at 75-100 rpm. A solution of sodium
hydroxide (2.0 kg) in
water (8.3 kg) was added over a period of about one hour. The reaction mixture
was then
stirred for 90 minutes at 21-26 °C and then was warmed to 85-100
°C for 90 minutes. The
i s reaction mixture was then cooled to 30-40 °C and adjusted to pH 4.3-
5.0 with HCl.
The reaction mixture was then filtered and the filtrate was heated at 121-130
°C in a
sealed vessel for 80-90 minutes. The solution was concentrated to a volume of
about 15 L and
cooled to ambient temperature. The iron-dextran solution was then slowly added
to 121 kg of
methanol over about 60 minutes with vigorous stirnng. A precipitate formed
instantly. The
2o solid was filtered and rinsed with methanol (120 kg) and then was suspended
in 64 kg of
methanol. The suspension was stirred for 30 minutes. The solid was filtered
and dried in
vacruo at 85 °C to give 4_03 kg of iron-dextran powder.
It is understood that the foregoing detailed description and accompanying
examples are
merely illustrative and are not to be taken as limitations upon the scope of
the invention, which
2s is defined solely by the appended claims and their equivalents. Various
changes and
rnodifications to the disclosed embodiments will be apparent to those skilled
in the art. Such
cha~lges and modifications, including without limitation those relating to the
materials and/or
methods of use of the invention, may be made without departing from the spirit
and scope
thereof.
