Pyrimethamine Tablets
Action and use
Dihydrofolate reductase inhibitor; antiprotozoal (malaria).
Definition
Pyrimethamine Tablets contain Pyrimethamine.
Content of pyrimethamine, C12H13ClN4
92.5 to 107.5% of the stated amount.
Identification
Shake a quantity of the powdered tablets containing 50 mg of Pyrimethamine with 50 mL of ethanol (96%) for 20 minutes, filter and evaporate the filtrate to dryness. The infrared absorption spectrum of the residue, Appendix II A, is concordant with the reference spectrum of pyrimethamine (RS 309).
Related substances
Carry out the method for thin-layer chromatography, Appendix III A, using the following solutions.
4 volumes of chloroform, 8 volumes of propan-1-ol, 12 volumes of glacial acetic acid and 76 volumes of toluene.
Any secondary spot in the chromatogram obtained with solution (1) is not more intense than the spot in the chromatogram obtained with solution (2) (0.25%).
Assay
Weigh and powder 20 tablets. To a quantity of the powdered tablets containing 25 mg of Pyrimethamine add 50 mL of hot 0.1m hydrochloric acid and heat on a water bath for 10 minutes, swirling occasionally. Mix with the aid of ultrasound for 30 minutes, remove and cool to room temperature. Add sufficient 0.1m hydrochloric acid to produce 100 mL, filter and dilute 5 mL of the filtrate to 100 mL with 0.1m hydrochloric acid. Measure the absorbance of the resulting solution at the maximum at 272 nm, Appendix II B, using 0.1m hydrochloric acid in the reference cell. Calculate the content of C12H13ClN4 taking 316 as the value of A(1%, 1 cm) at the maximum at 272 nm.