STABILIZED PHARMACEUTICAL COMPOSITION
BACKGROUND OF THE INVENTION
Administration of pharmaceutical compounds, particularly by injection, usually
requires a suitable solvent or delivery system to enable the composition to be administered to
a patient.
An ideal solvent must typically have the following properties :
1. it must be capable of solubilizing therapeutically effective amount of the active
agent to produce an effective composition.
2. it must be compatible with the active agent
3. it should be safe i.e. it should not cause any toxicity to the patient.
4. it should produce a composition having a good shelf life.
Many solvents while possessing most of the above advantageous qualities are not
especially efficient in solubilizing the pharmaceutical agent to enable an effective
composition for administration.
On the other hand numerous pharmaceutical agents are not sufficiently soluble in any
one solvent to enable the resulting composition to be effective. Therefore mixtures of two or
more solvents are quite commonly used in pharmaceutical industry to overcome the
limitations of a single solvent to solubilize the active agent. These co-solvent systems are
suitable for solubilizing many pharmaceutical agents which cannot otherwise be solubilized
or dispersed in a single solvent.
One example of a co-solvent system is a mixture of a polar solvent and a non-ionic
solvent, such as a mixture of a polyethylene glycol and Cremophor EL (polyethoxylated
castor oil). Cremophor EL is a condensation product of castor oil and ethylene oxide sold by
BASF.
Although these co-solvent systems can be effective in solubilizing many compounds,
they are not without their disadvantages. A commonly used co-solvent system used for many
pharmaceutical agents is a 50:50 mixture of ethanol and Cremophor EL. A potential problem
associated with such solvents is that acids, salts or other ionic impurities, as well as residual
water in the solvent or solvent system, even if within the acceptable limits, can catalyze the
degradation of the pharmaceutical agent. For example, co-solvents of ethanol and
Cremophor are known to result in particulates forming upon dilution with infusion solutions.
In addition, fibrous precipitates of unknown composition form in some formulations during
storage for extended periods of time.
A solvent with sufficiently low levels of particularly deleterious impurities will yield
a more stable pharmaceutical agent containing compositions. In particular, pharmaceutical
composition of Taxol the FDA approved composition of Paclitaxel marketed by Bristol
Myers Squibb in a co-solvent of 50:50 by volume of dehydrated ethanol and commercial
grade Cremophor EL exhibit a loss of potency of greater than 60% after storage for 12 weeks
at SO.degree C (US Patent 5,504,102). The loss of potency is attributed to the decomposition
of paclitaxel during storage. It is believed that carboxylate anions present in Cremophor EL
can catalyze the decomposition of paciltaxel, even at levels within the defined limits set forth
in the National Formulary. The U.S. Patent No. 5.504.102 (Agharkar et al) incorporated
herein by reference discloses removing the carboxylate anions from polyethoxylated castor
oils (cremophor) by acid addition or alumina adsorption.
Nikolayev et al in US Patent No. 5.925.776 discloses a method of reducing the cation
content in the polyethoxylated castor oil (cremophor). This is achieved by pre-treating the
polyethoxylated castor oil with a strong cation exchange resin. The low cationic content
polyethoxylated castor oil of the invention is then utilized to prepare formulations of various
agents which are found to be sensitive to the previously commercially available
polyethoxylated castor oil (cremophor EL). The stability of paclitaxel formulated in a
mixture of low cationic content polyethoxylated castor oil of the invention and ethyl alcohol
is shown to be better as compared to a formulation using untreated polyethoxylated castor oil
of the invention and ethyl alcohol.
Anevski et al in US Patent No. 6.388.112 discloses a process for purifying a non-ionic
surfactant or solvent capable of dispersing and solubilizing a pharmaceutical compound. In
the process, a solution of solvent and alcohol is brought in contact with an activated carbon
column and an ion exchange resin column. The process is particularly adapted to the
purification of polyethoxylated castor oils. The purified solvent is useful in the preparation
of pharmaceutic compositions having enhance shelf life, such as for use with paclitaxel.
Carver et al in US Patent No. 6.306.894 disloses a pharmaceutical formulation of
paclitaxel and polyethoxylated castor oilwherein the formulation is relatively acidified to a
pH of less than 8.1 and preferably within a pH range of 5 to 7, inclusively. Ethanol is
optionally included in the formulation. A formulation method is also disclosed and includes
the step of mixing an acid with a carrier material, such as polyethoxylated castor oil, to form
a carrier solution after which paclitaxel is added in an amount such that the resulting pH is
less than 8.1 and preferably in a pH range of 5 to 7. Ethanol may optionally be slurried with
the paclitaxel before mixing with the carrier solution.
A variety of acidifying agents, a preferred one being anhydrous citric acid, are
described. Acids in the form of powders, for example citric acid, have been preferred over
those which contain water, for example sulfuric acid. The most preferred acid for use in
accordance with the disclosed invention is citric acid, but a wide range of acids may be used
including :
Citric acid—monohydrous, Citric acid—anhydrous, Citric acid—hydrous, Acetic acid,
Formic acid, Ascorbic acid, Aspartic acid, Benzene sulphonic acid, Benzoic acid,
Hydrochloric acid, Sulphuric acid, Phosphoric acid, Nitric acid, Tartaric acid, Diatrizoic acid,
Glutamic acid, Lactic acid, Maleic acid, Succinic acid
Owens et al in US Patent No. 6.071.952 disloses a pharmaceutical composition with
long term storage stability comprising of a taxane or taxoid by incorporating an effective
amount of an antioxidant.
Previous efforts to develop a shelf stable composition of some pharmaceutical
compositions in various co-solvent systems have not been entirely successful. Thus, there is
a continuing need in the art for a solvent or co-solvent system capable of being used for
preparing stabilized compositions and, in particular, stabilized injection compositions
containing a pharmaceutical agent.
SUMMARY OF THE INVENTION
The invention is directed to a solvent suitable for preparing stabilized injection
compositions containing at least one pharmaceutical agent. Accordingly, it is a primary
object of the invention to provide a method of preparing a treated solvent having a stabilizing
effect on the composition and a method of preparing stabilized pharmaceutical compositions
using the treated solvent.
The stabilized pharmaceutical composition produced from the treated solvent of the
invention has been shown to have a shelf life greater than the compositions produced from
untreated solvent. The solvent system of the invention is particularly suitable for use with
pharmaceutical compounds that exhibit decomposition which is catalyzed by the presence of
ionic, metallic and oxidizing impurities. Of particular interest are the antineoplastic agents
such as paclitaxel, teniposide, camptothecin and derivatives thereof.
The solvent system of the invention essentially comprises an alcohol. The preferred
solvent includes absolute or dehydrated alcohol such as that sold by Merck. The absolute
alcohol is treated to reduce the ionic, metallic and oxidizing impurities to a sufficiently low
concentration to minimize the decomposition of the pharmaceutical agent that is catalyzed by
the presence of these impurities. The content of impurities of the absolute alcohol is lowered
by either treating the absolute alcohol with a strongly basic anion exchanger eg Amberlite
IRA 400 sold by Rohm and Haas Copmpany to separate the anionic as well as other
impurities or by the addition of a stabilizing agent possessing the combined properties of an
acidifying agent, a chelating agent as well as an antioxidant and particularly an organic acid
such as malic acid.
The advantages of the invention are also attained by producing a stabilized
pharmaceutical composition comprising at least one antineoplastic compound and a solvent
capable of solubilising the antineoplastic compound, the solvent comprising a solubilizing
amount of an alcohol such as absolute alcohol having been pre-treated to have an impurities
content sufficiently low to substantially prevent degradation of the antineoplastic compound.
Further advantages of the invention are attained by providing a method of stabilizing
a pharmaceutical composition containing a pharmaceutical agent selected from the group
consisting of paclitaxel, and a solvent containing pre-treated absolute ethanol and a
solubilizing agent. The solubilizing agent can be a condensation product of an alkylene oxide
and a lipid or fatty acid. The preferred solubilizing agent includes a polyoxyethylated castor
oil such as that sold by M/s BASF under the tradename Cremophor EL or Cremophor ELP
DETAILED DESCRIPTION OF THE INVENTION
The disadvantages and limitations of the previous injection composition and solvent
systems are overcome by the present invention while providing a convenient and efficient
method of producing a solvent and a method of stabilizing pharmaceutical compositions
suitable for injection. The present invention is primarily directed to a solvent suitable for
producing a stabilized pharmaceutical composition and to a method of producing and
stabilizing a pharmaceutical composition.
In the prior aitAgharkar et al in US Patent 5,504,102 give a disclosure that paclitaxel
reacts with ethanol during storage and that the decomposition of paclitaxel is catalyzed by the
carboxylate anions in the solvent. They also disclose that lowering the carboxylate
concentration of the solvent produced a stabilizing effect on the pharmaceutical composition.
The composition in question being Taxol, prepared as an injection concentrate containing 6
mg/ml paclitaxel in 50:50 by volume ethanol and polyoxyethylated castor oil, The
polyoxyethylated castor oil as being sold under the tradename Cremophor EL
As per their disclosure, the pharmaceutical agents of interest are those having an ester
linkage that can be cleaved by an alcohol in the presence of carboxylate anions. In their
preferred embodiments, the solvent is a co-solvent mixture of at least one solvent and a
solubilizing agent. The preferred solvent includes alcohol such as dehydrated ethanol. The
solubilizing agent in preferred embodiments is a polyoxyethylated castor oil such as that sold
under the tradename Cremophor EL or Cremophor ELP by BASF.
In their preferred embodiments, the carboxylate anion content of the solvent is
lowered by a number of methods. In one embodiment of the invention, the Cremophor EL or
other solvent is passed through a standard chromatography column of aluminum oxide which
adsorbs the carboxylate anions as well as other impurities to reduce the carboxylate anion
content of the solvent. In an alternative embodiment, the solvent is treated by the addition of
an acid in a stabilizing amount to reduce the carboxylate anion content to a sufficiently low
level to substantially prevent catalyzed degradation of the pharmaceutical compound.
Our invention provides a pharmaceutical stable formulation of paclitaxel. The
process consists of treating absolute alcohol such that the content of ionic, metallic and
oxidizing impurities of the alcohol can be lowered by a number of methods. In a first
embodiment of the invention, the alcohol is contacted with specified quantities of a strongly
basic anion exchange resin for specified time. This reduces the ionic impurities present in the
alcohol.
In an alternative embodiment of the invention, the alcohol is treated by the addition of
an organic acid and not a mineral acid, the preferred organic acid being Malic acid in a
stabilizing amount to reduce the ionic, metallic and oxidizing impurities content to a
sufficiently low level to substantially prevent degradation of the pharmaceutical compound
catalyzed by these impurities. The acid may be added to the alcohol before or after admixing
with the pharmaceutical compound. Mineral acids such as, for example, HC1, HBr, HF, HI,
H2SO4 and HNOa are not used as they are found to cause higher degradation of the drug than
in the absence of these acids. Alternatively, organic acids such as lactic acid, citric acid and
more preferably Malic acid may be used. Contrary to the disclosure by Agharkar et al that
the organic acids are generally less preferred since they can provide a source of carboxylate
anions to hinder the stabilizing effect of the acid treatment we find that Malic acid has a
much better stabilizing effect on the composition containing paclitaxel in absolute alcohol as
compared to a composition stabilized with a mineral acid.
Malic acid has this unique triple action property of being an antioxidant, a chelating
agent and an acidifying agent (Ref : Handbook of Pharmaceutical Excipients, 3rd ed, edited
by Arthur H. Kibbe; Pharmaceutical Press, UK). Formulations stabilized by the addition of
Malic acid also inhibits/slows down the degradation/polymerization of cremophor.
Malic acid as antioxidant:
Malic acid is an alpha hydroxy acid popularly used as antioxidant, chelating and
acidulating agents in many formulations. The antioxidative effect arises due to their ability to
scavenge free radicals formed during oxidation reactions. Even as they are effective in the
role of anti-oxidant effect per se, they are known to enhance antioxidative effect of other
compounds since they can chelate metal ions. Studies indicate that these compounds may
show an affinity for certain metal ions, for eg., malic acid can sequester aluminium ions
strongly.
Cremophor on long exposure to atmosphere decomposes to free fatty acids, glycerols
epoxidized oils and can also get polymerized. Malic acid, a free radical scavenger, stabilizes
cremophor. The addition of malic acid in the paclitaxel cremophor formulation stops further
degradation/polymerization of cremophor and thereby stabilizes the formulation.
Malic acid as chelating agent:
Malic acid also form chelates with the trace metals present in the solvent. The
tentative structure of the chelate can be shown as follows in which two carboxylate ion of the
malic acid can possibly play role as bidentate ligand
0 o
JL s* o
X Metal
•o"
1
MALIC ACID CHELATES
Malic acid and Alcohol improves Solvation :
The addition of alcohol and malic acid in the paclitaxel cremophor formulation can
enhance the stability due the solvation effect by forming intermolecular hydrogen bonding .
The side chain of paclitaxel have -OH groups which can easily form hydrogen bonding with
-COOH and -OH groups of malic acid and alcohol and further enhance the stability of the
formulation.
Structure of Cremophor:
Cremophor is polyethoxylated castor oil. The composition of fatty acids component
of castor oil are constant and approximately in following ratio

Ricinoleic acid:89.5%
Linoleic acid:4.2%
Oleicacid: 3.0%
Stearicacid: 1.0%
Palmitic acid: 1.0%
Dihydroxy stearic acid: 0.7%
Linolenic acid: 0.3%
Eicosanoic acid: 0.3%
All the hydroxy group of the fatty acids are polyethoxylated in cremophor. The structure of
cremophor which is a mixture of various triglycerides of different fatty acids can be
represented as follows;
Structure of Cremophor
Major population ~ 90%
Population ~ 4%
Population- 3%
Population- 2%
Population- 1.3%
The following non-limiting examples are intended to demonstrate the preferred embodiments
of the invention. One skilled hi the art will readily recognize that numerous embodiments of
the invention can be practiced to achieve the stabilizing effect.
Example -1
This example was carried out to demonstrate the effect of pre-treatment of absolute
alcohol with different types of ion exchange resins on the stability of Paclitaxel.
Sample la was prepared by dissolving 6 mg/ml of paclitaxel in absolute alcohol. The
Sample Ib was prepared by pre-treating the absolute alcohol with a strongly basic anion
exchange resin and then dissolving the paclitaxel in it to get a concentration of 6 mg/ml. The
Sample Ic was prepared by pre-treating the absolute alcohol with a strongly acidic cation
exchange resin and then dissolving the paclitaxel in it to get a concentration of 6 mg/ml. The
sample Id was prepared by pre-treating the absolute alcohol with a mixture of stongly acidic
cation exchange resin and strongly basic anion exchange resin and then dissolving the
paclitaxel in it to get a concentration of 6 mg/ml The samples were then subjected to an
accelerated degradation study at 50°C. The results obtained are summarized as below :

Table -1
Sample la
Sample Ib
Sample Ic
Sample Id
Degradation Products % at 50°C
Baccatin
2
Days
0.24
0.03
0.02
0.02
8
Days
0.45
0.21
0.06
0.06
EESC
2
Days
0.20
0.02
0.00
0.00
8
Days
0.37
0.17
0.02
0.02
10-DAP
2
Days
0.03
0.05
0.81
0.34
8
Days
0.17
0.07
1.83
1.03
10-DA-7-EP
2
Days
0.00
0.00
0.00
0.00
8
Days
0.00
0.00
0.00
0.00
7-EP
2
Days
0.28
0.17
0.24
0.14
8
Days
0.85
0.39
0.56
0.38
Total
(including
other
degradation
products)
2
Days
0.76
0.26
2.51
0.50
8
Days
1.83
0.84
5.52
2.30
EESC = Ethyl Ester Side Chain
10-DAP = 10 Deacetyl Paclitaxel
10-DA-7-EP = 10 Deacetyl 7 Epi-paclitaxel
7-EP = 7 Epi-paclitaxel
As shown in Table 1 - Sample Ib prepared with absolute alcohol pre-treated with
strongly basic anion exchange resin stabilizes paclitaxel maximum. Sample Ic prepared with
absolute alcohol pre-treated with strongly acidic cation exchange resin increases the
degradation of paclitaxel.
Example - 2
This example was carried out to demonstrate the effect of addition of mineral acid
versus organic acid to absolute alcohol on the stability of Paclitaxel.
A solution of Paclitaxel was prepared by dissolving 20 mg/ml of paclitaxel in absolute
alcohol. The solution was divided into 6 parts in 6 different vials. Each of the samples 2a to
2f were mixed with the components listed in the table 2 so as that the pH was adjusted
between 3.7 to 3.9. The samples were then subjected to an accelerated degradation study at
50°C and then analysed by HPLC for degradation products. The results obtained are
summarized as below:
11
Table - 2
Sample
2a
Sample
2b
Sample
2c
Sample
2d
Sample
2e
Sample 2f
Component
Added
None
HC1
(1%)
Malic Acid
HC1 +
Malic Acid
Lactic Acid
Citric Acid
pH
(10% soln
in water)
5.61
3.86
3.78
3.85
3.85
3.80
Percentage of Degradation Products after 2 days at 50°C
Baccatin
0.09
0.00
0.00
0.00
0.12
0.00
EESC
0.08
0.00
0.00
0.00
0.04
0.00
10-DAP
0.05
0.62
0.00
0.31
0.08
0.02
10-DA-7-EP
0.00
0.00
0.00
0.00
0.00
0.00
7-EP
0.20
0.11
0.11
0.09
0.17
0.15
Total
(including
other
degradation
products)
0.42
1.70
0.11
0.57
0.41
0.17
EESC = Ethyl Ester Side Chain
10-DAP = 10 Deacetyl Paclitaxel
10-DA-7-EP = 10 Deacetyl 7 Epi-paclitaxel
7-EP = 7 Epi-paclitaxel
As shown in Table 2 - Sample 2C stabilized with. Malic acid gives the maximum
stability. Hydrochloric acid on the other hand increases the degradation of Paclitaxel hi
alcoholic solution.
Example - 3
This example was carried out to demonstrate the effect of dialysis of solvent on the
stability of Paclitaxel in compositions prepared using solvent dialysed to remove low
molecular weight impurities including ionic, metallic and oxidative impurities.
Polyethoxylated castor oil sold under the brand name of Cremophor EL by BASF was
dialysed using dialysis tubing of regenerated cellulose of molecular weight cut-off of 3.5 KD
against dehydrated alcohol to remove low molecular weight impurities. Optionally,
dehydrated alcohol treated with a stabilizer possessing the unique properties of an
antioxidant, a chelating agent and an acidifying agent may be used for dialysis. The alcohol

was then removed from the dialysed samples using rota-evaporator. Compositions were then
prepared by dissolving 6 mg/ml of paclitaxel in 50:50 v/v mixture of dialysed Cremophor EL
and dehydrated alcohol. These samples were then subjected to an accelerated degradation
study at 50°C and then analysed by HPLC for degradation products. The results obtained are
summarized as below :
Table - 3
Sample 3a
Sample 3b
Cremophor- EL
Used
Undialysed
Dialysed-3.5KD
Percentage of Degradation Products after 2 days at 50°C
Baccatin
3.21
0.96
EESC
2.53
0.71
10-DAP
0.31
0.13
10-DA-7-EP
0.21
0.00
7-EP
1.38
0.44
Total
(including
other
degradation
products)
7.80
2.26
EESC = Ethyl Ester Side Chain
10-DAP = 10 Deacetyl Paclitaxel
10-DA-7-EP = 10 Deacetyl 7 Epi-paclitaxel
7-EP = 7 Epi-paclitaxel
As shown in Table 3 - Sample 3b prepared using dialysed cremophor shows lesser
extent of degradation as compared to composition prepared using un-dialysed cremophor.
Example - 4
This example was carried out to demonstrate the combined effect of pre-treatment of
absolute alcohol (as in example 1 and 2) and dialysis of Cremophor EL (as in example 3) or
Cremophor ELP on the stability of Paclitaxel
Compositions were prepared by dissolving 6 mg/ml of paclitaxel in 50:50 v/v mixture
of dialysed Cremophor ELP and pre-treated dehydrated alcohol. These samples were then
subjected to an accelerated degradation study at 50°C and then analysed by HPLC for
degradation products. The results obtained are summarized as below :
Table - 4
Percentage of Degradation Products at 50°C
13
Sample 4a
(Control)
Sample 4a
(Control)
Sample 4a
(Control)
Sample 4b
Cr-
ELP(Dialysed)/
EtOH (Pretreated)
Sample 4b
Cr-
ELP(Dialysed)/
EtOH (Pretreated)
Sample 4b
Cr-
ELP(Dialysed)/
EtOH (Pretreated)
(Initial)
(50°C for 1
Week)
(50°C for 3
Week)
(Initial)
(50°C for 1
Week)
(50°Cfor3
Week)
Baccatin
0.00
0.19
0.37
0.00
0.01
0.02
EESC
0.00
0.10
0.21
0.00
0.00
0.04
10-DAP
0.00
0.00
0.21
0.00
0.00
0.02
10-DA-7-EP
0.00
0.00
0.00
0.00
0.00
0.00
7-EP
0.08
0.14
0.31
0.10
0.09
0.11
Total
(including
other
degradation
products)
0.08
0.44
1.10
0.10
0.10
0.19
EESC = Ethyl Ester Side Chain
10-DAP = 10 Deacetyl Paclitaxel
10-DA-7-EP = 10 Deacetyl 7 Epi-paclitaxel
7-EP = 7 Epi-paclitaxel
As shown in Table 4 - Sample 4b prepared using dialysed Cremophor ELP and pretreated
alcohol shows much lesser extent of degradation as compared to control composition
prepared using un-dialysed Cremophor. ELP and untreated alcohol.
Example - 5
This example demonstrates a kit presentation for bedside reconstitution of the
Paclitaxel formulation. The presentation comprises two distinct containers, ampoules, a dual
chamber syringe, vials etc., one of which contains paclitaxel solution in a solvent preferably
dehydrated alcohol. The dehydrated alcohol may optionally be pre-treated as in examples 1

and 2 so as to have a stabilizing action on the stability of paclitaxel in the composition. The
other container, ampoule, chamber, vial contains a solubilizer that can be a polyethoxylated
castor oil (Cremophor EL or ELP) or a concentrate/combination of excipients that can help
keep the drug in solution when mixed together with a clinically acceptable aqueous dilution
fluid for infusion. The kit presentation also covers the combination of excipients suitable for
forming nanoparticles as disclosed in the US Patent No. 6,365,191 by the authors of this
invention.
It may be noted that the containers such as vials, ampoules, dual chamber syringes etc
are just mentioned as example and should not be taken as limiting examples. The basic
essence is to keep the two solutions i.e. the drug solution in the solvent and the solubilizer
separately till use so as to minimize the loss of potency of drug during shelf-life of the
product.