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

USP Reference standards 11— USP Bacitracin Zinc RS. USP Polymyxin B Sulfate 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 for bacitracin— Proceed with Ointment as directed in the Assay under Bacitracin Zinc Ointment.

Assay for polymyxin B— Proceed as directed for polymyxin B 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 Buffer No. 6. Combine the aqueous extracts, and dilute with Buffer No. 6 to an appropriate volume to obtain a stock solution. Dilute this stock solution quantitatively and stepwise with Buffer No. 6 to obtain a Test Dilution having a concentration assumed to be equal to the median dose level of the Standard.

Expert Committee : (MDANT05) Monograph Development-Antibiotics

USP29–NF24 Page 236

Phone Number : 1-301-816-8223