Packaging and storage— Preserve in tight containers.

USP Reference standards á11ñ— USP Erythromycin RS.

Identification— Prepare a test solution as follows.To 1g of Topical Gel in a 50-mLscrew-capped tube,add 20mLof 0.01Nhydrochloric acid,and heat in a water bath to reflux.Remove the tube from the water bath and shake it.Place the tube in the water bath again,and heat to reflux.Remove the tube from the water bath,and immediately decant a portion of the hot clear supernatant into a test tube.Allow to cool,add an equal volume of a mixture of methanol,water,and triethylamine (90:9:1),and mix.Concomitantly prepare a Standard solution as directed above,except to use 5mg of USP Erythromycin RSand 5mLof 0.01Nhydrochloric acid instead of 1g of Topical Gel and 20mLof 0.01Nhydrochloric acid.Separately apply 5µLof the test solution and the Standard solution to a thin-layer chromatographic plate (see Chromatography á621ñ),coated with a 0.25-mm layer of chromatographic silica gel.Place the plate in an unlined chromatographic chamber,and develop the chromatograms in a solvent system consisting of a mixture of methanol,water,and triethylamine (90:9:1)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the chromatographic chamber,mark the solvent front,and allow the solvent to evaporate.Spray the plate with a mixture of alcohol,p-methoxybenzaldehyde,and sulfuric acid (90:5:5).Heat the plate at 100for 10minutes,and examine the chromatograms.The spots due to erythromycin are black to purple in color:the RFvalue of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Minimum fill á755ñ: meets the requirements.

Assay— Proceed as directed under Antibiotics—Microbial Assays á81ñ,using an accurately weighed quantity of Topical Gel,equivalent to about 20mg of erythromycin,blended for about 3minutes in a high-speed glass blender jar containing 200.0mLof Buffer No.3to which has been added 0.5%of polysorbate 80.Dilute an accurately measured volume of the blended solution quantitatively 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 759

Phone Number:1-301-816-8335