Benzocaine, Butamben, and Tetracaine Hydrochloride 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

Benzocaine, Butamben, and Tetracaine Hydrochloride Ointment is Benzocaine, Butamben, and Tetracaine Hydrochloride in a suitable ointment base. It contains NLT 90.0% and NMT 110.0% of the labeled amounts of benzocaine (C₉H₁₁NO₂), butamben (C₁₁H₁₅NO₂), and tetracaine hydrochloride (C₁₅H₂₄N₂O₂·HCl).

2 IDENTIFICATION

A. The retention times of the major peaks of the Sample solution correspond to those of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Diluent: Methanol and water (60:40)

Mobile phase: Methanol, water, and 0.25 M sodium 1-heptanesulfonate (500:500:20)

Standard solution: Transfer 140 mg of USP Benzocaine RS to a 100-mL volumetric flask with the aid of 25 mL of methanol, and swirl. Transfer 140J mg of USP Butamben RS to the same volumetric flask with the aid of 25 mL of water, J being the ratio of the labeled amount, as a percentage, of butamben to the labeled amount, as a percentage, of benzocaine in the Ointment. Transfer 140J′ mg of USP Tetracaine Hydrochloride RS to the same volumetric flask with the aid of 25 mL of water, J′ being the ratio of the labeled amount, as a percentage, of tetracaine hydrochloride to the labeled amount, as a percentage, of benzocaine in the Ointment. Sonicate for about 1 min, and dilute with Diluent to volume.

Sample stock solution: Nominally 14 mg/mL of benzocaine, prepared as follows. Transfer a portion of Ointment, equivalent to 1400 mg of benzocaine, to a 100-mL volumetric flask. Add 75 mL of methanol, and mix. Sonicate for about 1 min, and dilute with methanol to volume.

Sample solution: Nominally 1.4 mg/mL of benzocaine in Diluent from the Sample stock solution

Chromatographic system

Mode: LC

Detector: UV 313 nm

Column: 3.9-mm × 30-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 10 µL

System suitability

Sample: Standard solution

[Note—The relative retention times for benzocaine, butamben, and tetracaine are about 0.3, 0.8, and 1.0, respectively.]

Suitability requirements

Resolution: NLT 2 between benzocaine and butamben, and between butamben and tetracaine

Relative standard deviation: NMT 2.0% for each of the three analyte peaks

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amounts of benzocaine (C₉H₁₁NO₂), butamben (C₁₁H₁₅NO₂), and tetracaine hydrochloride (C₁₅H₂₄N₂O₂·HCl) in the portion of Ointment taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of the corresponding analyte from the Sample solution

rₛ = peak response of the corresponding analyte from the Standard solution

Cₛ = concentration of the corresponding Reference Standard in the Standard solution (mg/mL)

Cᵤ = nominal concentration of the corresponding analyte in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

Minimum Fill 〈755〉: Meets the requirements

5 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, and avoid freezing.

USP Reference Standards 〈11〉

USP Benzocaine RS

USP Butamben RS

USP Tetracaine Hydrochloride RS