Packaging and storage— Preserve in well-closed containers.

Labeling— Label it to indicate that it is intended for veterinary use only.

USP Reference standardsá11ñ— USP Penicillin G Potassium RS.USP Neomycin Sulfate RS.USP Polymyxin B Sulfate RS.USP Hydrocortisone Acetate RS.

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 for penicillin G— Proceed as directed for penicillin Gunder Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Topical Suspension blended for 2minutes in a high-speed glass blender jar with 499.0mLof Buffer No.1and 1.0mLof polysorbate 80.Allow to stand for 10minutes,and dilute an accurately measured volume of the aqueous phase quantitatively and stepwise with Buffer No.1to obtain a Test Dilutionhaving a concentration of penicillin Gassumed to be equal to the median dose level of the Standard.

Assay for neomycin— Proceed as directed for neomycin under Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Topical Suspension 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.To an accurately measured volume of this stock solution add an accurately measured volume of penicillinase sufficient to inactivate the penicillin Gtherein,heat at 37for 30minutes,and dilute quantitatively and stepwise with Buffer No.3to obtain a Test Dilutionhaving a concentration of neomycin assumed to be equal to the median dose level of the Standard.

Assay for polymyxin B— Proceed as directed for polymyxin Bunder Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Topical Suspension blended for 2minutes in a high-speed glass blender jar containing 499.0mLof Buffer No.6and 1.0mLof polysorbate 80.Allow to stand for 10minutes,and to an accurately measured volume of the aqueous phase add an accurately measured volume of penicillinase sufficient to inactivate the penicillin Gtherein.Heat the solution at 37for 30minutes,and dilute quantitatively and stepwise with Buffer No.6to obtain a Test Dilutionhaving a concentration of polymyxin assumed to be equal to the median dose level of the Standard.Add to each test dilution of the Standard a quantity of USP Neomycin Sulfate RSdissolved in Buffer No.6to obtain the same concentration of neomycin present in the Test Dilution.

Assay for hydrocortisone acetate— Using an accurately measured volume of Topical Suspension,proceed as directed in the Assayunder Hydrocortisone Acetate Lotion.

Expert Committee:(VET)Veterinary Drugs

USP28–NF23Page 1495

Phone Number:1-301-816-8178