Bacitracin Zinc and Polymyxin B Sulfate Ointment

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION

Bacitracin Zinc and Polymyxin B Sulfate Ointment contains the equivalent of NLT 90.0% and NMT 130.0% of the labeled amounts of bacitracin and polymyxin B. It may contain a suitable local anesthetic.

2 IDENTIFICATION

A. THIN-LAYER CHROMATOGRAPHIC IDENTIFICATION TEST (201BNP): Meets the requirements

3 ASSAY

3.1 BACITRACIN

(See Antibiotics-Microbial Assays (81)).

Standard solution: Proceed as directed in the chapter. To each Test Dilution of the standard add sufficient hydrochloric acid to obtain the same concentration of hydrochloric acid as in the Test Dilution of Ointment.

Sample solution: Shake a portion of Ointment with about 50 mL of ether in a separator, and extract with four 20-mL portions of 0.01 N hydrochloric acid. Combine the acid extracts, and dilute with 0.01 N hydrochloric acid to a suitable volume.

Analysis: Proceed as directed in the chapter. Dilute the Sample solution with Buffer B.1 to obtain a Test Dilution having a bacitracin concentration that is nominally equivalent to the median level of the standard. Add sufficient hydrochloric acid to each Test Dilution of the standard to obtain the same concentration of hydrochloric acid as in the Test Dilution of the sample.

Acceptance criteria: 90.0%-130.0%

3.2 POLYMYXIN B

(See Antibiotics-Microbial Assays (81)).

Sample solution: Shake a portion of Ointment with about 50 mL of ether in a separator, and extract with four 20-mL portions of Buffer B.6 (see the chapter). Combine the buffer extracts, and dilute with Buffer B.6 to a suitable volume.

Analysis: Proceed as directed in the chapter. Dilute the Sample solution with Buffer B.6 to obtain a Test Dilution having a polymyxin B concentration that is nominally equivalent to the median level of the standard.

Acceptance criteria: 90.0%-130.0%

4 SPECIFIC TESTS

WATER DETERMINATION, Method (921)

Analysis: Use 20 mL of a mixture of toluene and methanol (7:3) in place of methanol in the titration vessel.

Acceptance criteria: NMT 0.5%

MINIMUM FILL (755): Meets the requirements

5 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed, light-resistant containers.

USP REFERENCE STANDARDS (11)

USP Bacitracin Zing RS

USP Polymyxin B Sulfate RS