Imiquimod

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

Imiquimod contains NLT 98.0% and NMT 102.0% of imiquimod (C₁₄H₁₆N₄), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. ▲Spectroscopic Identification Tests 〈197〉, Infrared Spectroscopy: 197K▲ (CN 1-May-2020)

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

3 ASSAY

Procedure

Buffer: 0.005 M sodium 1-octanesulfonate in water containing 0.1% triethylamine. Adjust with dilute perchloric acid to a pH of 2.0.

Mobile phase: Acetonitrile and Buffer (27:73)

Standard solution: 50 µg/mL of USP Imiquimod RS in Mobile phase

Sample solution: 50 µg/mL of Imiquimod in Mobile phase

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 226 nm

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

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Sample: Standard solution

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of imiquimod (C₁₄H₁₆N₄) in the portion of Imiquimod taken:

Result = (rᵤ / rₛ) × (Cₛ / Cᵤ) × 100

rᵤ = peak response from the Sample solution

rₛ = peak response from the Standard solution

Cₛ = concentration of USP Imiquimod RS in the Standard solution (µg/mL)

Cᵤ = concentration of Imiquimod in the Sample solution (µg/mL)

Acceptance criteria: 98.0%–102.0% on the dried basis

4 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.2%

Organic Impurities

Buffer: 0.005 M sodium octanesulfonate in water containing 0.1% triethylamine. Adjust with dilute perchloric acid to a pH of 2.0.

Diluent: Acetonitrile and Buffer (20:80)

Solution A: Buffer

Solution B: Acetonitrile

Mobile phase: See Table 1.

Table 1

Standard solution: 1.25 µg/mL each of USP Imiquimod Related Compound A RS, USP Imiquimod Related Compound B RS, USP Imiquimod Related Compound C RS, and USP Imiquimod RS in Diluent

Sample solution: 0.25 mg/mL of Imiquimod in Diluent

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 226 nm

Column: 4.6-mm × 25-cm; 5-µm packing L1

Column temperature: 45°

Flow rate: 1.5 mL/min

Injection volume: 20 µL

System suitability

Sample: Standard solution

Suitability requirements

Resolution: NLT 3 between imiquimod and imiquimod related compound C

Relative standard deviation: NMT 3.0% for imiquimod

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each known impurity in the portion of Imiquimod taken:

Result = (rᵢ / rᵣₛ) × (Cᵣₛ / Cᵤ) × 100

rᵢ = peak response of each known impurity from the Sample solution

rᵣₛ = peak response of the corresponding related compound from the Standard solution

Cᵣₛ = concentration of the corresponding Reference Standard in the Standard solution (µg/mL)

Cᵤ = concentration of Imiquimod in the Sample solution (µg/mL)

Calculate the percentage of any other impurity in the portion of Imiquimod taken:

Result = (rᵢ / rₛ) × (Cₛ / Cᵤ) × 100

rᵢ = peak response of each individual impurity from the Sample solution

rₛ = peak response of imiquimod from the Standard solution

Cₛ = concentration of USP Imiquimod RS in the Standard solution (µg/mL)

Cᵤ = concentration of Imiquimod in the Sample solution (µg/mL)

Acceptance criteria: See Table 2.

Table 2

5 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry a sample at 100°–105° for 3 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, and store at controlled room temperature.

USP Reference Standards 〈11〉

USP Imiquimod RS

USP Imiquimod Related Compound A RS

1-Isobutyl-1H-imidazo[4,5-c]quinoline

C₁₄H₁₅N₃ 225.29

USP Imiquimod Related Compound B RS

1-Isobutyl-1H-imidazo[4,5-c]quinoline 5-oxide

C₁₄H₁₅N₃O 241.29

USP Imiquimod Related Compound C RS

4-Chloro-1-isobutyl-1H-imidazo[4,5-c]quinoline

C₁₄H₁₄ClN₃ 259.73