Packaging and storage— Preserve in well-closed containers containing not more than 60 g, unless labeled solely for hospital use, preferably at controlled room temperature.

USP Reference standards 11— USP Bacitracin Zinc RS.

Thin-layer chromatographic identification test 201BNP: meets the requirements.

Minimum fill 755: meets the requirements.

Water, Method I 921: not more than 0.5%, 20 mL of a mixture of toluene and methanol (7:3) being used in place of methanol in the titration vessel.

Residual solvents 467: meets the requirements.

Assay— Proceed as directed under Antibiotics—Microbial Assays 81, using an accurately weighed portion of Ointment shaken with about 50 mL of ether in a separator, and extracted with four 20-mL portions of 0.01 N hydrochloric acid. Combine the acid extracts, and dilute with 0.01 N hydrochloric acid to an appropriate volume to obtain a stock solution. Dilute this stock solution quantitatively and stepwise with Buffer No. 1 to obtain a Test Dilution having a concentration assumed to be equal to the median dose level of the Standard, adding additional hydrochloric acid to each test dilution of the Standard to obtain the same concentration of hydrochloric acid as in the Test Dilution.

Expert Committee : (MDANT05) Monograph Development-Antibiotics

USP29–NF24 Page 236

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