Pramoxine Hydrochloride Cream

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

Pramoxine Hydrochloride Cream contains NLT 90.0% and NMT 110.0% of the labeled amount of pramoxine hydrochloride (C₁₇H₂₇NO₃ · HCl) in a suitable water-miscible base.

2 IDENTIFICATION

A.

Standard: 50 mg of USP Pramoxine Hydrochloride RS

Sample: Nominally 50 mg of pramoxine hydrochloride from a quantity of Cream

Analysis: Dissolve the Standard and the Sample separately in a mixture of 25 mL of methanol and 75 mL of ether, and extract each with three 25-mL portions of a mixture of equal volumes of 3 N hydrochloric acid and water. Discard the methanol–ether solutions, render the combined extracts alkaline with 25 mL of 5 N sodium hydroxide, and extract the pramoxine with 50 mL of chloroform. Evaporate the clear chloroform extracts with the aid of a current of air to dryness.

Acceptance criteria: The UV absorption spectrum of a solution (1 in 100,000) of the residue so obtained from the Sample, in 0.1 N hydrochloric acid, exhibits maxima and minima at the same wavelengths as that of a similar solution of the residue similarly obtained from the Standard.

B.

Sample: A 5-mg portion of the pramoxine obtained in Identification test A

Analysis: To the Sample add 1 drop of nitric acid. To the yellow solution cautiously add 5 drops of ammonium hydroxide. Acceptance criteria: A red-brown precipitate is formed.

3 ASSAY

Procedure

Buffer: Dissolve 3.5 g of dibasic potassium phosphate in 100 mL of water. Adjust the solution by the addition of phosphoric acid solution (1:1) to a pH of 7.5 ± 0.1.

Mobile phase: Acetonitrile, Buffer, and water (22:1:17)

Internal standard solution: 4 µL/mL of dibutyl phthalate in methanol

Standard stock solution: 2 mg/mL of USP Pramoxine Hydrochloride RS in methanol

Standard solution: Transfer 10 mL of the Standard stock solution and 5 mL of the Internal standard solution into a 100-mL volumetric ask, and dilute with methanol to volume.

Sample solution: Transfer nominally 18 mg of pramoxine hydrochloride from a portion of Cream to a glass-stoppered, 250-mL conical ask. Add 15.0 mL of isopropyl alcohol and 40.0 mL of methanol, and heat on a steam bath, with swirling, to dissolve the Cream. Add 40.0 mL of methanol and 5.0 mL of the Internal standard solution. Cool the flask to a temperature of 10° or less to precipitate the waxes, and filter the solution.

3.1 Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 224 nm

Columns

Guard: 4.6-mm × 3-cm; packing L1

Analytical: 4-mm × 30-cm; packing L1

Flow rate: 2 mL/min

Injection volume: 20 µL

3.2 System suitability

Sample: Standard solution

[Note—The relative retention times for pramoxine hydrochloride and dibutyl phthalate are about 0.8 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 2.4 between pramoxine hydrochloride and dibutyl phthalate

Relative standard deviation: NMT 2.0% in three replicate injections

3.3 Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of pramoxine hydrochloride (C₁₇H₂₇NO₃ · HCl) in the portion of Cream taken:

Result = (R_U /R_S ) × (C_S /C_U ) × 100

R_U = peak response ratio of pramoxine hydrochloride to the internal standard from the Sample solution

R_S = peak response ratio of pramoxine hydrochloride to the internal standard from the Standard solution 

C_S = concentration of USP Pramoxine Hydrochloride RS in the Standard solution (mg/mL)

C_U = nominal concentration of pramoxine hydrochloride in the Sample solution (mg/mL)

Acceptance criteria: 90.0%–110.0%

4 PERFORMANCE TESTS

Minimum Fill 〈755〉: Meets the requirements

5 SPECIFIC TESTS

Microbial Enumeration Tests 〈61〉andTests for Specified Microorganisms 〈62〉: It meets the requirements of the tests for the absence of Staphylococcus aureus and Pseudomonas aeruginosa.

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers.

USP Reference Standards 〈11〉

USP Pramoxine Hydrochloride RS