Polymyxin B Sulfate and Bacitracin Zinc Topical Powder
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
Polymyxin B Sulfate and Bacitracin Zinc Topical Powder contains not less than 90.0 percent and not more than 130.0 percent of the labeled amounts of polymyxin B and bacitracin.
Packaging and storage—Preserve in well-closed containers.
USP Reference standards 〈11〉—
USP Bacitracin Zinc RS
USP Polymyxin B Sulfate RS
Microbial enumeration tests 〈61〉 and Tests for specified microorganisms 〈62〉—Collect aseptically in a suitable container about 1 g from not less than 5 containers, dissolve in 500 mL of Fluid A, filter through a membrane filter as directed for Membrane Filtration under Test for Sterility of the Product to be Examined under Sterility Tests 〈71〉, except to place the filter on the surface of Soybean–Casein Digest Agar Medium in a Petri dish, incubate for 7 days at 30° to 35°, and count the number of colonies on the filter. Similarly prepare a second specimen, except to incubate at 20° to 25°. Not more than 20 colonies are observed from the two specimens. It meets also the requirements of the tests for absence of Staphylococcus aureus and Pseudomonas aeruginosa under Microbial Enumeration Tests 〈61〉 and Tests for specied microorganisms 〈62〉. Water Determination, Method I 〈921〉: not more than 7.0%.
Assay for polymyxin B—Proceed as directed for polymyxin B under Antibiotics—Microbial Assays 〈81〉, using an accurately weighed portion of Topical Powder, equivalent to about 5000 USP Polymyxin B Units, shaken with 20 mL of water in a suitable volumetric flask. Dilute with Buffer B.6 to volume, and mix. Dilute an accurately measured volume of the solution so obtained quantitatively with Buffer B.6 to obtain a Test Dilution having a concentration of polymyxin B assumed to be equal to the median dose level of the Standard.
Assay for bacitracin—Proceed as directed for bacitracin under Antibiotics—Microbial Assays 〈81〉, using an accurately weighed portion of Topical Powder, equivalent to about 800 USP Bacitracin Units, added to a 100-mL volumetric flask, dilute with 0.01 N hydrochloric acid to volume, and mix. Dilute this solution quantitatively with Buffer B.1 to obtain a Test Dilution having a concentration assumed to be equal to the median dose level of the Standard. In preparing each test dilution of the Standard, add additional hydrochloric acid to each to obtain the same concentration of hydrochloric acid as in the Test Dilution.
