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

USP Reference standards á11ñ— USP Bacitracin Zinc RS.

Thin-layer chromatographic identification test á201BNPñ: meets the requirements.

Minimum fill á755ñ: meets the requirements.

Water,Method Iá921ñ: not more than 0.5%,20mLof a mixture of toluene and methanol (7:3)being used in place of methanol in the titration vessel.

Assay— Proceed as directed under Antibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Ointment shaken with about 50mLof ether in a separator,and extracted with four 20-mLportions of 0.01Nhydrochloric acid.Combine the acid extracts,and dilute with 0.01Nhydrochloric acid to an appropriate volume to obtain a stock solution.Dilute this stock solution quantitatively and stepwise with Buffer No.1to obtain a Test Dilutionhaving 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:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 216

Phone Number:1-301-816-8335