Benzocaine Otic Solution

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 Otic Solution contains NLT 90.0% and NMT 110.0% of the labeled amount of benzocaine (C₉H₁₁NO₂).

2 IDENTIFICATION

A. The retention time of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

B. The UV spectrum of the major peak of the Sample solution corresponds to that of the Standard solution, as obtained in the Assay.

3 ASSAY

Procedure

Solution A: 0.1% Trifluoroacetic acid, prepared by diluting 1.0 mL of trifluoroacetic acid with water to 1 L

Solution B: Acetonitrile

Mobile phase: See Table 1.

Diluent: Solution A and Solution B (1:1)

System suitability solution: 1 µg/mL each of USP Benzocaine RS, USP Aminobenzoic Acid RS, and USP Ethyl 4-Nitrobenzoate RS in Diluent. Sonicate to dissolve, if necessary.

Standard solution: 0.1 mg/mL of USP Benzocaine RS in Diluent. Sonicate to dissolve, if necessary.

Sample solution: Nominally 0.1 mg/mL of benzocaine in Diluent prepared as follows. Transfer a portion of Otic Solution, equivalent to 10 mg of benzocaine, into a 100-mL volumetric flask and dissolve it in Diluent.

Chromatographic system

Mode: LC

Detector: UV 280 nm. For Identification test B, use a diode array detector in the range of 200–400 nm.

Column: 4.6-mm × 25-cm; 5-µm packing L7

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Samples: System suitability solution and Standard solution

Suitability requirements

Resolution: NLT 6 between aminobenzoic acid and benzocaine, and between benzocaine and ethyl 4-nitrobenzoate, System suitability solution

Tailing factor: NMT 1.5, Standard solution

Relative standard deviation: NMT 1.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of benzocaine (C₉H₁₁NO₂) in the portion of Otic Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of benzocaine from the Sample solution

rₛ = peak response of benzocaine from the Standard solution

Cₛ = concentration of USP Benzocaine RS in the Standard solution (mg/mL)

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

Acceptance criteria: 90.0%–110.0%

4 IMPURITIES

Organic Impurities

Solution A, Solution B, Mobile phase, Diluent, and Chromatographic system: Proceed as directed in the Assay.

Standard solution: 1 µg/mL each of USP Benzocaine RS, USP Aminobenzoic Acid RS, and USP Ethyl 4-Nitrobenzoate RS in Diluent. Sonicate to dissolve, if necessary.

Sample solution: Nominally 0.5 mg/mL of benzocaine in Diluent prepared as follows. Transfer a portion of Otic Solution, equivalent to 50 mg of benzocaine, into a 100-mL volumetric flask, dissolve, and dilute with Diluent to volume.

System suitability

Sample: Standard solution

[Note—See Table 2 for relative retention times.]

Suitability requirements

Resolution: NLT 6 between aminobenzoic acid and benzocaine, and between benzocaine and ethyl 4-nitrobenzoate

Relative standard deviation: NMT 3.0% for each peak corresponding to benzocaine, aminobenzoic acid, and ethyl 4-nitrobenzoate

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of aminobenzoic acid and ethyl 4-nitrobenzoate in the portion of Otic Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of aminobenzoic acid or ethyl 4-nitrobenzoate from the Sample solution

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

Cₛ = concentration of USP Aminobenzoic Acid RS or USP Ethyl 4-Nitrobenzoate RS in the Standard solution (mg/mL)

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

Calculate the percentage of any individual unspecified degradation product in the portion of Otic Solution taken:

Result = (rᵤ/rₛ) × (Cₛ/Cᵤ) × 100

rᵤ = peak response of any individual unspecified degradation product from the Sample solution

rₛ = peak response of benzocaine from the Standard solution

Cₛ = concentration of USP Benzocaine RS in the Standard solution (mg/mL)

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

Acceptance criteria: See Table 2. Disregard peaks less than 0.05%.

5 SPECIFIC TESTS

Microbial Enumeration Tests 〈61〉 and Tests for Specified Microorganisms 〈62〉: It meets the requirements of the tests for absence of Salmonella species and Escherichia coli and for absence of Staphylococcus aureus and Pseudomonas aeruginosa. The total aerobic microbial count is less than 10² cfu/mL.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers.

USP Reference Standards 〈11〉

USP Aminobenzoic Acid RS

Benzoic acid, 4-amino. C₇H₇NO₂ 137.14

USP Benzocaine RS

USP Ethyl 4-Nitrobenzoate RS

Benzoic acid, 4-nitro-, ethyl ester. C₉H₉NO₄ 195.17