Packaging and storage— Preserve in collapsible tubes or other tight containers,and avoid exposure to excessive heat.

USP Reference standards á11ñ— USP Gentamicin Sulfate RS.

Identification— Shake a quantity of Ointment,equivalent to about 5mg of gentamicin,with a mixture of 200mLof chloroform and 5mLof water.Allow to separate,and filter the aqueous layer:the filtrate so obtained meets the requirements of the Identificationtest under Gentamicin Injection.

Minimum fill á755ñ: meets the requirements.

Water,Method Iá921ñ: not more than 1.0%,20mLof a mixture of toluene and methanol (7:3)being used in place of methanol in the titration vessel.

Assay— Proceed with Ointment as directed under Antibiotics—Microbial Assays á81ñ,using an accurately weighed quantity of Ointment,equivalent to about 1mg of gentamicin,shaken with about 50mLof ether in a separator,and extracted with four 20-mLportions of Buffer No.3.Combine the aqueous extracts,and dilute quantitatively and stepwise with Buffer No.3to obtain a Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard.

Expert Committee:(PA7)Pharmaceutical Analysis 7

USP28–NF23Page 897

Phone Number:1-301-816-8335