Mefenamic Acid Tablets
Action and use
Cyclo-oxygenase inhibitor; analgesic; anti-inflammatory.
Definition
Mefenamic Acid Tablets contain Mefenamic Acid.
Content of mefenamic acid, C15H15NO2
95.0 to 105.0% of the stated amount.
Identification
Extract a quantity of the powdered tablets containing 0.25 g of Mefenamic Acid with two 30-mL quantities of ether. Wash the combined extracts with water, evaporate to dryness on a water bath and dry the residue at 105°. Dissolve a sufficient quantity in the minimum volume of absolute ethanol and evaporate to dryness on a water bath. The infrared absorption spectrum, Appendix II A, is concordant with the reference spectrum of mefenamic acid (RS 210).
Tests
2,3-Dimethylaniline
Carry out the method for thin-layer chromatography, Appendix III A, using a TLC silica gel G plate and a mixture of 1 volume of 18m ammonia, 25 volumes of 1,4-dioxan and 90 volumes of toluene as the mobile phase. Apply separately to the plate 40 µL of each of the following solutions. For solution (1) shake a quantity of the powdered tablets containing 0.25 g of Mefenamic Acid with a mixture of 7.5 mL of dichloromethane and 2.5 mL of methanol for 10 minutes, centrifuge and use the supernatant liquid. Solution (2) contains 0.00025% w/v of 2,3-dimethyl-aniline in a mixture of 3 volumes of dichloromethane and 1 volume of methanol. After removal of the plate, dry it in a current of warm air and visualise by Method I. Any spot corresponding to 2,3-dimethylaniline in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (100 ppm).
Related substances
Carry out the method for thin-layer chromatography, Appendix III A, using a TLC silica gel GF254 plate and a mixture of 1 volume of glacial acetic acid, 25 volumes of 1,4-dioxan and 90 volumes of toluene as the mobile phase. Apply separately to the plate 20 µL of each of the following solutions. For solution (1) use the supernatant liquid obtained in the test for 2,3-Dimethylaniline. For solution (2) dilute 1 volume of solution (1) to 500 volumes with a mixture of 3 volumes of dichloromethane and 1 volume of methanol. After removal of the plate, allow it to dry in air, expose to iodine vapour for 5 minutes and examine under ultraviolet light (254 nm). Any secondary spot in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (0.2%). Disregard any spot with an Rf value of 0.04 or less.
Assay
Weigh and powder 20 tablets. Dissolve a quantity of the powdered tablets containing 0.5 g of Mefenamic Acid in about 80 mL of warm absolute ethanol previously neutralised to phenol red solution alternating between heating and ultrasound to aid dissolution. Cool, add sufficient of the neutralised absolute ethanol to produce 100 mL, mix well and titrate with 0.1m sodium hydroxide VS using phenol red solution as indicator. Each mL of 0.1m sodium hydroxide VS is equivalent to 24.13 mg of C15H15NO2.