Antipyrine and 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

Antipyrine and Benzocaine Otic Solution is a solution of Antipyrine and Benzocaine in Glycerin. It contains NLT 90.0% and NMT 110.0% of the labeled amount of antipyrine (C₁₁H₁₂N₂O) and benzocaine (C₉H₁₁NO₂)

[NOTE-In the preparation of this Otic Solution, use Glycerin that has a low water content, in order that the Otic Solution may comply with the limit for Water Determination. This may be ensured by using Glycerin having a specific gravity of NLT 1.2607, corresponding to a concentration of 99.5%.]

2 IDENTIFICATION

A. The UV spectrum of the antipyrine and benzocaine peaks of the Sample solution exhibit maxima and minima at the same wavelengths as those of the Standard solution, as obtained in the Assay.

B. 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

Solution A: 50 mM monobasic potassium phosphate and 0.2% triethylamine. Adjust with 10 N sodium hydroxide to a pH of 7.0.

Solution B: Acetonitrile

Mobile phase: See Table 1.

Table 1

Diluent: Acetonitrile and water (1:1)

Standard solution: 0.014 mg/mL of USP Benzocaine RS and 0.054 mg/mL of USP. Antipyrine RS in Diluent

Sample solution: Nominally 0.014 mg/mL of benzocaine and 0.054 mg/mL of antipyrine prepared as follows. Transfer a suitable quantity of Otic Solution to a suitable volumetric flask. Dilute with Diluent to volume.

Chromatographic system

(See Chromatography (621). System Suitability.)

Mode: LC

Detector: UV 270 nm. For Identification A, use a diode array detector in the range of 200-400 nm.

Column: 4.6-mm x 15-cm; 5-µm packing LZ

Flow rate: 1 mL/min.

Injection volume: 20 µL

System suitability

Sample: Standard solution

[NOTE-See Table 2 for the relative retention times for antipyrine and benzocaine.]

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of antipyrine (C₁₁H₁₂N₂O) and benzocaine (C₉H₁₁NO₂) in the portion of Otic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × 100

r_u = peak response of antipyrine or benzocaine from the Sample solution

r_s = peak response of antipyrine or benzocaine from the Standard solution

C_s = concentration of USP Antipyrine RS or USP Benzocaine RS in the Standard solution (mg/mL)

C_u = nominal concentration of antipyrine or benzocaine in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 IMPURITIES

ORGANIC IMPURITIES

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

System suitability solution: 0.1 mg/mL of USP Antipyrine RS and 0.01 mg/mL of USP Antipyrine Related Compound A RS in Diluent

Standard solution: 0.001 mg/mL each of USP Benzocaine RS and USP Ethyl 4-Nitrobenzoate RS, and 0.004 mg/mL of USP Antipyrine RS in

Diluent

Sample solution: Nominally 3.2 mg/mL of antipyrine and 0.8 mg/mL of benzocaine prepared as follows. Transfer a suitable quantity of Otic

Solution to a suitable volumetric flask. Dilute with Diluent to volume.

System suitability

Samples: System suitability solution and Standard solution

[NOTE-See Table 2 for the relative retention times.]

Suitability requirements

Resolution: NLT 2.0 between antipyrine related compound A and antipyrine, System suitability solution

Relative standard deviation: NMT 5%, Standard solution

Analysis

Samples: Standard solution and Sample solution

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

Result = (r_u /r_s ) × (C_s /C_u ) × 100

r_u = peak response of ethyl 4-nitrobenzoate from the Sample solution

r_s = peak response of ethyl 4-nitrobenzoate from the Standard solution

C_s = concentration of USP Ethyl 4-Nitrobenzoate RS in the Standard solution (mg/mL)

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

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

Result = (r_u /r_s ) × (C_s /C_u ) × 100

r_u = peak response of each individual, unspecied degradation product from the Sample solution

r_s = peak response of benzocaine from the Standard solution

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

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

Acceptance criteria: See Table 2. Disregard any impurity peaks less than 0.1%.

Table 2

^a Process impurities are controlled in the drug substance and are not to be reported here. They are not included in the calculation of total impurities.

^b Specied impurity related to benzocaine.

LIMIT OF AMINOBENZOIC ACID

Solution A: Glacial acetic acid and water (1:69)

Solution B: Methanol

Mobile phase: See Table 3.

Table 3

Diluent: Solution A and Solution B (9:1)

Standard solution: 0.001 mg/mL of USP Aminobenzoic Acid RS in Diluent

Sample solution: Nominally 3.2 mg/mL of antipyrine and 0.8 mg/mL of benzocaine prepared as follows. Transfer a suitable quantity of Otic

Solution to a suitable volumetric flask. Dilute with Diluent to volume.

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 280 nm

Column: 3.0-mm × 15-cm; 3.5-µm packing 111

Flow rate: 0.4 mL/min

Injection volume: 5 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 5.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of aminobenzoic acid in the portion of Otic Solution taken:

Result = (r_u /r_s ) × (C_s /C_u ) × 100

r_u = peak response of aminobenzoic acid from the Sample solution

r_s = peak response of aminobenzoic acid from the Standard solution

C_s = concentration of USP Aminobenzoic Acid RS in the Standard solution (mg/mL)

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

Acceptance criteria: NMT 0.2%

5 SPECIFIC TESTS

Water Determination 〈921〉, Method I: NMT 1.0%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight, light-resistant containers. Store at controlled room temperature.

USP Reference Standards 〈11〉

USP Aminobenzoic Acid RS

p-Aminobenzoic acid.

C₇H₇NO₂ 137.14

USP Antipyrine RS

USP Antipyrine Related Compound A RS

3-Methyl-1-phenyl-1H-pyrazol-5(4H)-one.

C₁₀H₁₀N₂O 174.20

USP Benzocaine RS

USP Ethyl 4-Nitrobenzoate RS

Ethyl p-nitrobenzoate.

C₉H₉NO₄ 195.17