Packaging and storage— Preserve in tight, light-resistant containers.

USP Reference standards 11—
USP Sulfamethizole RS.

Identification— Place a quantity of Oral Suspension, equivalent to about 500 mg of sulfamethizole, in a 50-mL centrifuge tube; add about 30 mL of water; mix; and centrifuge the mixture. Decant and discard the supernatant. Resuspend the residue in 15 mL of water, mix, and centrifuge the mixture. Decant and discard the clear supernatant. Repeat the washing procedure an additional two times. Dissolve the residue in a mixture of 10 mL of 6 N ammonium hydroxide and 10 mL of water, and filter. Warm the filtrate until most of the ammonia is expelled, cool, and add 6 N acetic acid until the mixture is distinctly acid: a precipitate of sulfamethizole is formed. Collect the precipitate on a filter, wash it well with cold water, and dry at 105 for 2 hours: the sulfamethizole so obtained responds to Identification test A under Sulfamethizole.

Uniformity of dosage units 905—

Deliverable volume 698—

Assay— Transfer an accurately measured volume of Oral Suspension, equivalent to about 500 mg of sulfamethizole, to a beaker. Add 50 mL of water and 20 mL of hydrochloric acid, stir until dissolved, cool to 15, and slowly titrate with 0.1 M sodium nitrite VS, determining the endpoint potentiometrically, using suitable electrodes. Each mL of 0.1 M sodium nitrite is equivalent to 27.03 mg of sulfamethizole (C9H10N4O2S2).

Topic/Question	Contact	Expert Committee
Monograph	Behnam Davani, Ph.D., M.B.A. Senior Scientist 1-301-816-8394	(MDAA05) Monograph Development-Antivirals and Antimicrobials
Reference Standards	Lili Wang, Technical Services Scientist 1-301-816-8129 RSTech@usp.org

USP32–NF27 Page 3625