Packaging and storage—
Preserve in well-closed containers,preferably at controlled room temperature.
Thin-layer chromatographic identification test á201BNPñ:
meets the requirements.
Assay for neomycin—
Proceed as directed under
Antibiotics—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 of
Buffer No.3.Combine the aqueous extracts,and dilute with
Buffer No.3to an appropriate volume to obtain a stock solution of convenient concentration.Dilute this stock solution quantitatively and stepwise with
Buffer No.3to obtain a
Test Dilution having a concentration assumed to be equal to the median dose level of the Standard.
Assay for polymyxin B—
Proceed as directed under
Antibiotics—Microbial Assays á81ñ,using an accurately weighed portion of Cream shaken with about 50mLof ether in a separator,and extracted with four 25-mLportions of
Buffer No.6.Combine the aqueous extracts,and dilute with
Buffer No.6to an appropriate volume to obtain a stock solution.Dilute this stock solution quantitatively and stepwise with
Buffer 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 in
Buffer No.6,to obtain the same concentration of neomycin present in the
Test Dilution.