Pyrimethamine Tablets

General Notices

Action and use

Dihydrofolate reductase inhibitor; antiprotozoal (malaria).

Definition

Pyrimethamine Tablets contain Pyrimethamine.

The tablets comply with the requirements stated under Tablets and with the following requirements.

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.

(1) Shake a quantity of the powdered tablets containing 50 mg of Pyrimethamine with 5 mL of a mixture of 9 volumes of chloroform and 1 volume of methanol and filter.
(2) Dilute 1 volume of solution (1) to 400 volumes with the same solvent mixture.
chromatographic conditions
(a) Use as the coating silica gel F254.
(b) Use the mobile phase as described below.
(c) Apply 20 µL of each solution.
(d) Develop the plate to 10 cm.
(e) After removal of the plate, allow it to dry in air and examine under ultraviolet light (254 nm).
mobile phase

4 volumes of chloroform, 8 volumes of propan-1-ol, 12 volumes of glacial acetic acid and 76 volumes of toluene.

limits

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.