Packaging and storage— Preserve in well-closed containers.

USP Reference standards á11ñ— USP Oxytetracycline RS.USP Polymyxin B Sulfate RS.

Minimum fill á755ñ: meets the requirements.

Loss on drying á731ñ— Dry about 100mg,accurately weighed,in a capillary-stoppered bottle in vacuum at a pressure not exceeding 5mm of mercury at 60for 3hours:it loses not more than 2.0%of its weight.

Assay for oxytetracycline— Transfer a suitable,accurately weighed quantity of Topical Powder to a glass blender jar containing a sufficient,accurately measured volume of 0.1Nhydrochloric acid to yield a stock solution containing not less than 150µg of oxytetracycline per mL,and blend at high speed for 3to 5minutes.Proceed as directed for oxytetracycline under Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of this solution diluted quantitatively and stepwise with water to obtain a Test Dilutionhaving a concentration of oxytetracycline assumed to be equal to the median dose level of the Standard.

Assay for polymyxin B— Transfer an accurately weighed quantity of Topical Powder,equivalent to about 10,000USP Polymyxin B Units,to a 50-mLcentrifuge tube,add 15mLof acetone and 0.05mLof hydrochloric acid,and stir.Add 20mLof acetone,and centrifuge for 10minutes.Decant and discard the clear liquid.Add 15mLof acetone and 0.05mLof hydrochloric acid to the residue,stir,add 20mLof acetone,and centrifuge for 10minutes,decanting and discarding the clear liquid.[NOTE—Take care not to discard any of the residue with the clear liquid.]Add 5mLof Buffer No.6to the residue,and mix.Transfer the mixture to a 100-mLvolumetric flask with the aid of Buffer No.6,dilute with the same solvent to volume,and mix.Proceed as directed for polymyxin Bunder Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of this stock solution diluted quantitatively with Buffer No.6to obtain a Test Dilutionhaving a concentration of polymyxin Bassumed to be equal to the median dose level of the Standard.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 1453

Phone Number:1-301-816-8335