Metronidazole Gel

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

Metronidazole Gel contains NLT 90.0% and NMT 110.0% of the labeled amount of metronidazole (C₆H₉N₃O₃).

2 IDENTIFICATION

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

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

Solution A: Methanol and water (20:80)

Solution B: Methanol

Mobile phase: See Table 1.

Table 1

System suitability solution: 0.6 µg/mL of USP Metronidazole RS and 0.6 µg/mL of USP Tinidazole Related Compound A RS in Solution A

Standard solution: 30 µg/mL of USP Metronidazole RS in Solution A

Sample stock solution: Nominally 300 µg/mL of metronidazole in Solution A prepared as follows. Transfer a portion of Gel to a suitable volumetric flask. Add Solution A equivalent to 50% of the flask volume and sonicate or vortex until dissolved. Dilute with Solution A to volume. [NOTE-On the basis of formulation, if necessary, centrifuge a portion of the solution at 3000 rpm for 10 min and pass a portion of the supernatant through a filter of 0.45-µm pore size. Use the filtrate.]

Sample solution: Nominally 30 µg/mL of metronidazole in Solution A prepared from the Sample stock solution

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 319 nm. For Identification test A, use a diode-array detector in the range of 210-500 nm.

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

Column temperature: 30°

Flow rate: 1 mL/min

Injection volume: 30 µL

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 metronidazole and tinidazole related compound A, System suitability solution

Tailing factor: NMT 2.0, Standard solution

Relative standard deviation: NMT 2.0%, Standard solution

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of the labeled amount of metronidazole (C₆H₉N₃O₃) in the portion of Gel taken:

                         Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of metronidazole from the Sample solution

r_S = peak response of metronidazole from the Standard solution S

C_S = concentration of USP Metronidazole RS in the Standard solution (µg/mL) 

C_U = nominal concentration of metronidazole in the Sample solution (µg/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.

Standard solution: Use the System suitability solution from the Assay.

Sample solution: Use the Sample stock solution from the Assay.

System suitability

Sample: Standard solution

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

Suitability requirements

Resolution: NLT 2.0 between metronidazole and tinidazole related compound A

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of tinidazole related compound A in the portion of Gel taken:

                         Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of tinidazole related compound A from the Sample solution

r_S = peak response of tinidazole related compound A from the Standard solution

C_S = concentration of USP Tinidazole Related Compound A RS in the Standard solution (µg/mL) 

C_U = nominal concentration of metronidazole in the Sample solution (µg/mL)

Calculate the percentage of each individual unspecified impurity in the portion of Gel taken:

                         Result = (r_U/r_S) × (C_S/C_U) × 100

r_U = peak response of each unspecified impurity from the Sample solution

r_S = peak response of metronidazole from the Standard solution 

C_S = concentration of USP Metronidazole RS in the Standard solution (µg/mL)

C_U = nominal concentration of metronidazole in the Sample solution (µg/mL)

Acceptance criteria: See Table 2.

Table 2

5 PERFORMANCE TESTS

MINIMUM FILL (755): Meets the requirements

6 SPECIFIC TESTS

PH (791): The apparent pH determined potentiometrically is between 4.0 and 6.5.

7 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in laminated collapsible tubes at controlled room temperature.

USP REFERENCE STANDARDS (11)

USP Metronidazole RS

USP Tinidazole Related Compound A RS

2-Methyl-5-nitroimidazole.

C₄H₅N₃O₂               127.10