Packaging and storage— Preserve in tight containers.

USP Reference standards á11ñ— USP Erythromycin RS.

Identification— Prepare a test solution by mixing a portion of the Topical Solution with methanol to obtain a concentration of about 2.5mg of erythromycin per mL.Proceed as directed in the Identificationtest under Erythromycin Delayed-Release Capsules,beginning with “Prepare a Standard solution of USP Erythromycin RS.”

Water,Method Iá921ñ: not more than 8.0%if it contains 20mg per mL,or not more than 5.0%if it contains 15mg per mL,or not more than 2.0%if it contains acetone,20mLof a mixture of pyridine and methanol (1:1)being used in place of methanol in the titration vessel.

Alcohol content,Method IIá611ñ: between 92.5%and 107.5%of the labeled amount of C2H5OH.

Assay— Proceed as directed under Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Topical Solution diluted quantitatively with Buffer No.3to yield 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 761

Phone Number:1-301-816-8335