Packaging and storage— Preserve in well-closed containers,preferably at controlled room temperature.

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

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

Minimum fill á755ñ: meets the requirements.

Assay for neomycin— Proceed as directed underAntibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Cream,equivalent to about 1.75mg of neomycin,shaken in a separator with about 50mLof ether,and extracted with four 20-mLportions ofBuffer No.3.Combine the aqueous extracts,and dilute withBuffer No.3to an appropriate volume to obtain a stock solution of convenient concentration.Dilute this stock solution quantitatively and stepwise withBuffer No.3to obtain aTest Dilution having a concentration assumed to be equal to the median dose level of the Standard.

Assay for polymyxin B— Proceed as directed underAntibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Cream shaken with about 50mLof ether in a separator,and extracted with four 25-mLportions ofBuffer No.6.Combine the aqueous extracts,and dilute withBuffer No.6to an appropriate volume to obtain a stock solution.Dilute this stock solution quantitatively and stepwise withBuffer No.6to obtain a Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard (10Polymyxin B Units per mL).Add to each test dilution of the Standard a quantity of USP Neomycin Sulfate RS,dissolved inBuffer No.6,to obtain the same concentration of neomycin present in theTest Dilution.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 1351

Phone Number:1-301-816-8335