Metronidazole

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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C₆H₉N₃O₃          171.15

1H-Imidazole-1-ethanol, 2-methyl-5-nitro-;

2-Methyl-5-nitroimidazole-1-ethanol      CAS RN^®: 443-48-1; UNII: 140QM0216E.

1 DEFINITION

Metronidazole contains NLT 99.0% and NMT 101.0% of metronidazole (C₆H₉N₃O₃), calculated on the dried basis.

2 IDENTIFICATION

Change to read:

A. ^▲SPECTROSCOPIC IDENTIFICATION TESTS (197), Infrared Spectroscopy: 197K-A _{▲(CN 1-MAY-2020)} Meets the requirements

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

Mobile phase: Methanol and water (1:4)

Standard solution: 0.03 mg/mL of USP Metronidazole RS in Mobile phase

Sample solution: 0.03 mg/mL of Metronidazole in Mobile phase

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 319 nm.

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

Column temperature: 30°

Flow rate: 1 mL/min

Injection volume: 30 µL

Run time: Twice the retention time of metronidazole

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 metronidazole (C₆H₉N₃O₃) in the portion of Metronidazole taken: 33

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

r_U = peak response from the Sample solution

r_S = peak response from the Standard solution 

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

C_U = concentration of Metronidazole in the Sample solution (mg/mL)

Acceptance criteria: 99.0%-101.0% on the dried basis

4 IMPURITIES

4.1 RESIDUE ON IGNITION (281)

NMT 0.1%

4.2 ORGANIC IMPURITIES

Mobile phase and Chromatographic system: Proceed as directed in the Assay. The run time is 30 min.

Standard solution: 1 µg/mL of metronidazole from USP Metronidazole RS and 2 µg/mL of tinidazole related compound A from USP Tinidazole Related Compound A RS in Mobile phase

Sample solution: 1.0 mg/mL of Metronidazole in Mobile phase

System suitability

Sample: Standard solution

[NOTE-See Table 1 for the relative retention times.]

Suitability requirements

Resolution: NLT 2.0 between tinidazole related compound A and metronidazole

Tailing factor: NMT 2.0 for the metronidazole peak

Relative standard deviation: NMT 6.0% for both tinidazole related compound A and metronidazole; six replicate injections

Analysis

Samples: Standard solution and Sample solution

Calculate the percentage of tinidazole related compound A in the portion of Metronidazole 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 (mg/mL)

C_U = concentration of Metronidazole in the Sample solution (mg/mL)

Calculate the percentage of any single unspecified impurity in the portion of Metronidazole taken:

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

r_U = peak response of any single 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 (mg/mL) 

C_U = concentration of Metronidazole in the Sample solution (mg/mL)

Acceptance criteria: See Table 1.

Table 1

5 SPECIFIC TESTS

LOSS ON DRYING (731)

Analysis: Dry at 105° for 2 h.

Acceptance criteria: NMT 0.5%

6 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Preserve in well-closed, light-resistant containers, and store at controlled room temperature.

USP REFERENCE STANDARDS (11)

USP Metronidazole RS

USP Tinidazole Related Compound A RS

2-Methyl-5-nitroimidazole.

C₄H₅N₃O₂           127.10