Diclofenac sodium injection sterilized by autoclave and the occurrence of cyclic reaction producing a small amount of impurity

Article abstract of DOI:10.1002/1520-6017(200105)90:5<541::AID-JPS1011>3.0.CO;2-O

A known impurity is formed in the production of a parenteral dosage form of diclofenac sodium if terminally sterilized by autoclave. This impurity has been detected as 1-(2,6-diclorophenyl) indolin-2-one, which is also an intermediate from which diclofenac sodium is generally synthesized. It is only the condition of the autoclave method (i.e., 123 ± 2°C) that enforces the intramolecular cyclic reaction of diclofenac sodium forming the indolinone derivative and sodium hydroxide. The formation of this impurity has been found to depend on the initial pH of the formulation. The reaction follows first-order kinetics, and the energy of activation is 5.34 kcal/mol. The other excipients in the formulation do not have a role in this reaction. The concentration of the impurity in the resultant product in the ampule goes beyond the limit of the raw materials in the pharmacopoeias. It is thus preferable to use an alternative sterilization method; that is, an aseptic filtration method in which the formation of this impurity can be avoided.

Full text of DOI:10.1002/1520-6017(200105)90:5<541::AID-JPS1011>3.0.CO;2-O

Diclofenac Sodium Injection Sterilized by Autoclave and
the Occurrence of Cyclic Reaction Producing a Small
Amount of Impurity
JIBEN ROY, MAFIZUL ISLAM, ANOWAR H. KHAN, SUBODH C. DAS, M. AKHTERUZZAMAN, AJAY K. DEB,
A. H. MAHBUB ALAM
Department of Quality Control & Product Development and Chemicals Division, Square Pharmaceuticals Limited,
Square Centre, 48 Mohakhali C/A, Dhaka-1212, Bangladesh
Received 27 December 1999; revised 20 July 2000; accepted 26 October 2000
ABSTRACT: A known impurity is formed in the production of a parenteral dosage form of
diclofenac sodium if terminally sterilized by autoclave. This impurity has been detected
as 1-(2,6-diclorophenyl) indolin-2-one, which is also an intermediate from which diclo-
fenac sodium is generally synthesized. It is only the condition of the autoclave method
ꢀ
(
i.e., 123 Æ 2 C) that enforces the intramolecular cyclic reaction of diclofenac sodium
forming the indolinone derivative and sodium hydroxide. The formation of this impurity
has been found to depend on the initial pH of the formulation. The reaction follows ®rst-
order kinetics, and the energy of activation is 5.34 kcal/mol. The other excipients in the
formulation do not have a role in this reaction. The concentration of the impurity in the
resultant product in the ampule goes beyond the limit of the raw materials in the
pharmacopoeias. It is thus preferable to use an alternative sterilization method; that is,
an aseptic ®ltration method in which the formation of this impurity can be avoided.
ß 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:541±544, 2001
Keywords: diclofenac sodium; injection; sterilization; impurity; reaction kinetics;
intramolecular cyclization
INTRODUCTION
aseptic ®ltration method or by terminal autoclav-
ing under heat and pressure, provided the product
is stable under the autoclaving conditions. The
validated terminal sterilization processes achieve
Diclofenac sodium [2-(2,6-dichloroanilino) phe-
nyl] acetate (Figure 1), a commonly used nonste-
roidal antiin¯ammatory drug, is manufactured
via a stable intermediate, 1-(2,6-dichlorophenyl)
indolin-2-one, which is commonly known as the
indolinone derivative, by heating in the presence
of sodium hydroxide. The impurity level of the
indolinone derivative in diclofenac sodium raw
material is limited to only 0.2% mentioned in the
�
6
a high degree of sterility assurance (1 in 10
)
compared with aseptic processing methods (1 in
�
3 2
10 ). Thus, a natural tendency of the pharma-
ceutical companies is to go for the most assured
terminal autoclave method. Regarding heat sta-
bility of diclofenac sodium in solution, there is one
3
report in which a solution of diclofenac sodium
1
ꢀ
British Pharmacopoeia (BP). Among the various
had been kept at 71 C for 201 days and 75.3% of
dosage forms of diclofenac sodium, the parenteral
dosage form is also very popular. In general, injec-
tion in the ampule form is sterilized either by the
the diclofenac sodium degraded. The recommen-
ded storage conditions for the parenteral dosage
form of diclofenac sodium stated to protect ampu-
4
les for injection from heat and light. To our know-
ledge, there are no reports on the stability of
diclofenac sodium under autoclaving conditions.
In the case of parenteral dosage form of diclofenac
sodium, both sterilization procedures (i.e., term-
Correspondence to: Jiben Roy
E-mail: jiben@squaregroup.com)
(
Journal of Pharmaceutical Sciences, Vol. 90, 541±544 (2001)
ß 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 90, NO. 5, MAY 2001
541

5
42
ROY ET AL.
The excipients included benzyl alcohol (0.12 mL),
ethanol 96% (0.15 mL), propylene glycol (0.75
mL), sodium metabisul®te (9.00 mg), mannitol
(
18.00 mg), disodium edetate (0.3 mg), sodium
hydroxide (3.15 mg), and water for injection
quantity required to make 3 mL).
(
Autoclaving Conditions
ꢀ
The autoclaving conditions were 123 Æ 2 C at 1.1
2
kg/cm pressure for 25 to 30 min.
Figure 1. High performance liquid chromatograms
of (A) typical parenteral formulation before autoclave
and (B) after autoclave. Column: Zorbex ODS (4.6 Â 250
mm); Mobile phase: methanol: phosphate buffer (66:34);
Flow rate: 1.5/mL/min, UV 254 nm; Chart speed:
Effect of Initial pH on the Formation
of the Indolinone Derivative
The effect of the initial pH of the typical formula-
tion of the diclofenac sodium injection on the
extent of formation of the indolinone derivative
was detemined at pH 8, 9, 10, 11, and 12.
0
.5 cm/min
inal autoclave or aseptic ®ltration method) are
practiced in Bangladesh. In the Bangladesh drug
market, this parenteral form of diclofenac sodium
is available under different brand names. Screen-
ing the marketed products revealed the presence
of indolinone as an impurity in some brands, but
some brands were free of this impurity.
The objective of this work, therefore, was to
study the sources of this indolinone impurity in
the injectable ampule form. This analytical study
was carried out using a typical formulation, accor-
ding to the Scheme 1.
Reaction Kinetics Studies
A typical formulated diclofenac sodium injection
was used for the determination of the speci®c
reaction rate constant at different temperatures
and reaction activation energy. The ampules thus
prepared were placed at different temperatures
using an oven WC HERAEUS HANAU, Type
ꢀ
FTU340, with temperature range 30±220 C. The
experimental temperatures included 103, 123,
ꢀ
1
33, and 143 C for 0 to 83 min duration.
Different speci®c reaction constants at various
EXPERIMENTAL SECTION
Materials
elevated temperatures were obtained by plotting
the log of the concentration of indolinone deriva-
tives against time. Then, the logarithms of the
speci®c rates of formation of indolinone deriva-
tives were plotted against the reciprocals of the
absolute temperatures. From the slope of the best-
The sample of diclofenac sodium with potency
9
9.3% was supplied by the Chemicals Division of
Square Pharmaceuticals Ltd. All the other exci-
pients were of BP grade. HPLC grade methanol
was obtained from E. Merck. Double-distilled
water was used throughout the work.
®
tted straight line of the Arrhenius plot, the
activation energy (E ) was determined.
a
Typical Formulation
Analysis
Diclofenac sodium injection (75 mg/3 mL) was
formulated using diclofenac sodium BP (75 mg).
Reversed-phase high-performance liquid chroma-
tography (HPLC) analysis of diclofenac sodium
and its different formulations were carried out
using a Shimadzu LC-10 as pump, a Shimadzu
SPD-10A UV detector, a Shimadzu C-R 6A inte-
grator, and a Rheodyne-7125 injector. A reversed-
phase column (Zorbex ODS, 4.6 mm i.d.
 250 mm) was used for analysis. The mobile
phase consisted of 66% (v/v) methanol and 34%
phosphate buffer of pH 2.5, adjusted by adding
acetic acid. The overall analysis was conducted
1
Scheme 1.
according to the BP.
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 90, NO. 5, MAY 2001

DICLOFENAC SODIUM IMPURITY FORMATION DURING AUTOCLAVE STERILIZATION
543
RESULTS AND DISCUSSION
Diclofenac sodium powder used in this study was
analyzed by HPLC and found to be free from
indolinone impurity and had 99.3% potency. Typi-
cal formulated diclofenac sodium injection was
initially (before autoclave) free from any impur-
ity, including indolinone derivative; however,
after autoclave, 1.7% indolinone derivative was
detected. On the other hand, no such impurity
was detected in the same formulated injection
when the injectables were sterilized by aseptic
Figure 2. Formation of indolinone derivative from
diciofenac sodium.
two times consecutively, the amount of indolinone
derivative formed was increased compared with
the amount formed in single autoclave. At the
same time, pH of the resultant solution of the
doubled autoclaving was increased compared
with the pH of single autoclave (Table 1).
®
ltration processes. Typical HPLC chromato-
grams are shown in Figure 1.
To exclude any role of excipients in the for-
mation of indolinone derivative while autoclav-
ing, a solution of diclofenac sodium formulated
only in distilled water was prepared and analyzed
before and after autoclaving. The HPLC analysis
again indicated the presence of indolinone in the
later sample. When autoclaving was done at
It appears from the results in Table 1 that the
increase of pH as well as formation of indolinone
derivative occurred to a lesser extent in the
typical parenteral formulation of diclofenac
sodium, than in the formulation of diclofenac
sodium in water only. This difference is because
the typical injectable formulation contained
NaOH and the pH was higher to start with: thus,
the formation of more NaOH as well as the
production of indolinone derivative was inhibited.
In fact, the concentration of indolinone derivative
formed during autoclaving decreases as the initial
pH of the formulation increase (Figure 3). It may
be noted that the typical diclofenac sodium
injection formulations are not possible at lower
pH (i.e., at < 7) because of the conversion of
diclofenac sodium to insoluble diclofenac acid.
The intramolecular cyclization reaction of
diclofenac sodium producing the indolinone deri-
vative under the autoclaving condition (i.e., at
5
ꢀ
relatively lower temperature (i.e., at 116 Æ 1 C
for 30 min, the formation of indolinone derivative
was reduced to 0.7%, as expected. On the other
hand, there was no detectable degradation of
diclofenac sodium to indolinone derivative impur-
ꢀ
ity after heating at 83 C for 100 min.
Based on these results, we can reasonably pro-
pose that the intramolecular cyclic reaction of
diclofenac sodium under autoclaving condition
(
i.e., heat) produces the indolinone derivative
according to the probable mechanism depicted in
Figure 2. The reaction shown in Figure 2 also
indicates that the intramolecular cyclization of
diclofenac sodium also produces NaOH; therefore,
the pH of the resulting solution after autoclaving
should be higher than that of initial solution be-
fore autoclaving. In fact, this difference was
noted. The diclofenac sodium in distilled water
with pH 7.94 changed to pH 10.89 after autoclav-
ing. In addition, when the autoclaving was done
ꢀ
123 C) follows ®rst-order kinetics, and the activa-
tion energy in typical injection formulation at pH
8.41 is 5.34 kcal/mol. The formation of indolinone
derivative in the typical diclofenac sodium injec-
tion formulation at different temperatures as a
Table 1. Change of pH and Indolinone Derivative Impurity on Autoclaving
pH before autoclave pH after single autoclave
pH after double autoclave
(conc. of indolinone
derivative)
(conc. of indolinone
(conc. of indolinone
derivative)
Sample
derivative)
Diclofenac sodium injection
in typical formulation,
8.24, clear
solution (nil)
8.30, clear
solution (1.7%)
Ð
75 mg/3 mL
Diclofenac sodium injection
in water only, 75 mg/2 mL
Diclofenac sodium injection
in water only, 75 mg/3 mL
8.06, clear
solution (nil)
7.94, clear
10.70, turbid
solution (3.3%)
10.89, turbid
solution (3.9%)
Ð
11.13, turbid
solution (5.2%)
solution (nil)
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 90, NO. 5, MAY 2001

5
44
ROY ET AL.
Figure 5. Arrhenious plot showing temperature
dependence of reaction rates of indolinone derivative
formation.
Figure 3. Plot showing the effect of initial pH on the
formation of indolinone derivation.
function of time is shown in Figure 4, and the
corresponding Arrhenius plot showing tempera-
ture dependence of reaction rates of indolinone
derivative formation is given in Figure 5. The
relatively low energy of activation found in the
formation of indolinone derivative from diclofenac
sodium suggests that the reaction follows the most
favorable intramolecular substitution nucleophi-
lic cyclization mechanisms, as shown in Figure 2.
can be formed if the ampule for injection is steri-
lized terminally by the autoclave method. As long
as the level of impurity conforms to the speci®ca-
tions of the pharmacopoeia, there is no problem in
using the autoclave method for sterilizing ampu-
les for injection of diclofenac sodium. However,
the marketed samples that were monitored con-
tained, impuri®es at levels 4 to 9 times higher
than the individual impurity level mentioned in
the diclofenac sodium raw material in BP. Thus,
the aseptic ®ltration method is preferable because
it does not cause the formation of the indolinone
derivative impurity at all. The future edition of
BP or United States Pharmacopoeia (USP) should
include the speci®cations and the allowable limits
of impurities for the ampule form of diclofenac
sodium.
CONCLUSION
The indolinone derivative impurity in some
samples of marketed diclofenac sodium injection
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1
. British Pharmacopoeia, 1999. The British Pharma-
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2
. Avis KE, Lieberman HA, Lachman L. 1993. Phar-
maceutical dosage forms: Parental Medications,
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Pharm 74:85±93.
3
4
. Lund W, editor. 1994. The pharmaceutical codex.
London: The Pharmaceutical Press, p.836.
Figure 4. Formation of indolinone derivative in
diclofenac sodium injection at different temperature
as a function of time.
5. Ansel HC, Popovich NG. 1990. Pharmaceutical
dosage forms and drug delivery systems, Fifth
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JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 90, NO. 5, MAY 2001