Action and use
K epoxide reductase inhibitor; oral anticoagulant (coumarin).
DEFINITION
Warfarin Oral Suspension is a suspension of Warfarin Sodium in a suitable flavoured vehicle.
The oral suspension complies with the requirements stated under Oral Liquids and with the following requirements.
Content of warfarin sodium, C19H15NaO4
95.0 to 105.0% of the stated amount.
IDENTIFICATION
In the Assay, the retention time of the principal peak in the chromatogram obtained with solution (1) is similar to that of the principal peak in the chromatogram obtained with solution (2).
TESTS
Acidity
pH, 2.7 to 4.0, Appendix V L.
Related substances
Carry out the method for liquid chromatography, Appendix III D, using the following solutions.
(1) To a quantity of the oral suspension containing 10 mg of Warfarin Sodium add 30 mL of acetonitrile and mix; add 50 mL of water, mix with the aid of ultrasound for 10 minutes and allow the solution to cool to room temperature. Add sufficient water to produce 100 mL, mix and filter through a 0.45-μm cellulose acetate filter (GD/X is suitable).
(2) Dissolve 10 mg of 4-hydroxycoumarin (warfarin impurity B) in 50 mL of acetonitrile and add sufficient water to produce 100 mL. Dilute 1 volume of this solution to 10 volumes with a mixture containing 30 volumes of acetonitrile and 70 volumes of water and further dilute 1 volume to 10 volumes with the same mixture of solvents.
(3) Dissolve 10 mg of benzalacetone (warfarin impurity C) in 50 mL of acetonitrile and add sufficient water to produce 100 mL. Dilute 1 volume of this solution to 10 volumes with a mixture containing 30 volumes of acetonitrile and 70 volumes of water and further dilute 1 volume to 10 volumes with the same mixture of solvents.
(4) Dissolve 10 mg of (5RS)-3-(2-hydroxyphenyl)-5-phenylcyclohex-2-enone BPCRS (warfarin impurity A) in 50 mL of acetonitrile and add sufficient water to produce 100 mL. Dilute 1 volume of this solution to 10 volumes with a mixture containing 30 volumes of acetonitrile and 70 volumes of water and further dilute 1 volume to 10 volumes with the same mixture of solvents.
(5) Dissolve 80 mg of benzoic acid in 50 mL of acetonitrile and add sufficient water to produce 100 mL. Dilute 1 volume of this solution to 10 volumes with a mixture containing 30 volumes of acetonitrile and 70 volumes of water and further dilute 1 volume to 10 volumes with the same mixture of solvents.
(6) Mix equal volumes of solution (2) and solution (5).
CHROMATOGRAPHIC CONDITIONS
(a) Use a stainless steel column (15 cm × 4.6 mm) packed with phenylhexylsilyl silica gel for chromatography (5 μm) (Phenomenex Luna Phenyl-Hexyl is suitable) fitted with a stainless steel guard column (4 mm × 3 mm) packed with octadecylsilyl silica gel for chromatography.
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 2 mL per minute.
(d) Use a column temperature of 35°.
(e) Use a detection wavelength of 283 nm.
(f) Inject 50 μL of each solution.
When the chromatograms are recorded under the prescribed conditions the retention time of warfarin is about 19 minutes.
MOBILE PHASE
1 volume of acetic acid, 50 volumes of methanol and 50 volumes of water.
SYSTEM SUITABILITY
The test is not valid unless, in the chromatogram obtained with solution (6), the resolution factor between the peaks corresponding to 4-hydroxycoumarin and benzoic acid is at least 1.5.
LIMITS
In the chromatogram obtained with solution (1):
the area of any peaks corresponding to 4-hydroxycoumarin, benzalacetone and (5RS)-3-(2-hydroxyphenyl)-5- phenylcyclohex-2-enone are not greater than half the area of the principal peaks in the chromatograms obtained with solutions (2), (3) and (4) respectively (0.5% of each);
the area of any other secondary peak is not greater than 0.2 times the area of the principal peak in the chromatogram obtained with solution (2) (0.2%).
Disregard any peak corresponding to the peak in the chromatogram obtained with solution (5).
ASSAY
Carry out the method for liquid chromatography, Appendix III D, using the following solutions.
(1) To a weighed quantity of the oral suspension containing 10 mg of Warfarin Sodium add 30 mL of acetonitrile and mix; add 50 mL of water, mix with the aid of ultrasound for 10 minutes and allow the solution to cool to room temperature. Add sufficient water to produce 100 mL, mix and filter through a 0.45-μm cellulose acetate filter (GD/X is suitable).
(2) Dissolve 0.1 g of warfarin BPCRS in 100 mL of a mixture of equal volumes of acetonitrile and water; dilute 10 volumes of this solution to 100 volumes with a mixture containing 30 volumes of acetonitrile and 70 volumes of water.
CHROMATOGRAPHIC CONDITIONS
(a) Use a stainless steel column (15 cm × 4.6 mm) packed with phenylhexylsilyl silica gel for chromatography (5 μm) (Phenomenex Luna Phenyl-Hexyl is suitable) fitted with a stainless steel guard column (4 mm × 3 mm) packed with octadecylsilyl silica gel for chromatography.
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 2 mL per minute.
(d) Use a column temperature of 35°.
(e) Use a detection wavelength of 283 nm.
(f) Inject 50 μL of each solution.
MOBILE PHASE
1 volume of acetic acid, 50 volumes of methanol and 50 volumes of water.
DETERMINATION OF CONTENT
Determine the weight per mL of the oral suspension, Appendix V G, and calculate the content of C19H15NaO4, weight in volume, using the declared content of C19H16O4 in warfarin BPCRS. Each mg of C19H16O4 is equivalent to 1.071 mg of C19H15NaO4.
STORAGE
Warfarin Oral Suspension should be protected from light.
