Imiquimod 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

Imiquimod Cream contains NLT 90% and NMT 110% of the labeled amount of imiquimod (C₁₄H₁₆N₄).

2 IDENTIFICATION

Change to read:

A. ▲Spectroscopic Identification Tests 〈197〉, Ultraviolet-Visible Spectroscopy: 197U▲ (CN 1-May-2020)

Wavelength range: 220–400 nm

Diluent: Acetonitrile and 0.1 N hydrochloric acid (30:70)

Standard solution: 2 µg/mL of USP Imiquimod RS in Diluent. Sonicate, if necessary, to dissolve.

Sample stock solution: Nominally 20 µg/mL of imiquimod in Diluent prepared as follows. Transfer a portion of Cream equivalent to 5 mg of imiquimod into a 250-mL volumetric flask. Add about 60% of the flask volume of Diluent and sonicate for 30 min with occasional swirling to dissolve, if necessary. Dilute with Diluent to volume.

Sample solution: Nominally 2 µg/mL of imiquimod from Sample stock solution in Diluent. Pass through a suitable filter.

Acceptance criteria: The UV absorption spectrum of the Sample solution exhibits maxima and minima at the same wavelengths as that of the Standard solution.

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: 1.17 g/L of sodium 1-octanesulfonate in water. Add 1 mL of triethylamine for each liter of solution and adjust with perchloric acid to a pH of 2.5.

Mobile phase: Acetonitrile and Buffer (270:730)

Diluent: Acetonitrile and 0.1 N hydrochloric acid (30:70)

Standard stock solution: 0.2 mg/mL of USP Imiquimod RS in Diluent. Sonicate to dissolve, if necessary.

Standard solution: 0.01 mg/mL of USP Imiquimod RS in Mobile phase from Standard stock solution.

Sample stock solution: Nominally 0.2 mg/mL of imiquimod in Diluent prepared as follows. Transfer a portion of Cream equivalent to about 50 mg of imiquimod into a 250-mL volumetric flask. Add about 60% of the flask volume of Diluent, sonicate for 30 min with occasional swirling to dissolve, and cool if necessary. Dilute with Diluent to volume.

Sample solution: Nominally 0.01 mg/mL of imiquimod from Sample stock solution in Mobile phase. Pass through a suitable filter.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 226 nm

Column: 4.6-mm × 15-cm; 5-µm packing L7

Column temperature: 30°

Flow rate: 1.5 mL/min

Injection volume: 10 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 the labeled amount of imiquimod (C₁₄H₁₆N₄) in the portion of Cream taken:

Result = (rᵤ / rₛ) × (Cₛ / Cᵤ) × 100

rᵤ = peak response of imiquimod from the Sample solution

rₛ = peak response of imiquimod from the Standard solution

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

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

Acceptance criteria: 90%–110%

4 PERFORMANCE TESTS

Minimum Fill 〈755〉: Meets the requirement

5 IMPURITIES

Organic Impurities

Solution A: 1.17 g/L of sodium 1-octanesulfonate in water. Add 1 mL of triethylamine for each liter of solution and adjust with perchloric acid to a pH of 2.5.

Solution B: Acetonitrile and methanol (90:10)

Mobile phase: See Table 1.

Table 1

Diluent: Acetonitrile and 0.1 N hydrochloric acid (30:70)

Standard stock solution: 0.5 mg/mL of USP Imiquimod RS in Diluent. Sonicate to dissolve, if necessary.

Standard solution: 0.5 µg/mL of USP Imiquimod RS from Standard stock solution in Diluent.

Sample solution: Nominally 0.5 mg/mL of imiquimod prepared as follows. Transfer a portion of Cream equivalent to 25 mg of imiquimod into a 50-mL volumetric flask. Add about 30 mL of Diluent, and sonicate for 40 min with occasional swirling. Dilute with Diluent to final volume. Pass through a suitable filter.

Chromatographic system

(See Chromatography 〈621〉, System Suitability.)

Mode: LC

Detector: UV 240 nm

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

Column temperature: 50°

Flow rate: 1 mL/min

Injection volume: 20 µL

System suitability

Samples: Standard stock solution and Standard solution

Suitability requirements

Tailing factor: NMT 2.0, Standard stock solution

Relative standard deviation: NMT 5.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of each impurity in the portion of Cream taken:

Result = (rᵢ / rₛ) × (Cₛ / Cᵤ) × (1/F) × 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 (mg/mL)

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

F = relative response factor (see Table 2)

Acceptance criteria: See Table 2. Disregard any peak below 0.05%.

Table 2

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

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

ᶜ Process impurities monitored in the drug substance and not included in the calculation of total impurities.

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

6 SPECIFIC TESTS

pH 〈791〉

Sample: Nominally 2.5 mg/mL of imiquimod from Cream in water. Sonicate to disperse with constant swirling.

Acceptance criteria: 4.5–7.0

Microbial Enumeration Tests 〈61〉 and Tests For Specified Microorganisms 〈62〉:

The total aerobic microbial count is NMT 10² cfu/g, and the total yeasts and molds count is NMT 10¹ cfu/g. It meets the requirements for absence of S. aureus and P. aeruginosa.

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in tight containers, and store at 4°–25°. Protect from freezing.

USP Reference Standards 〈11〉

USP Imiquimod RS