Metronidazole Benzoate Compounded Oral Suspension

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 Benzoate Compounded Oral Suspension contains NLT 90.0% and NMT 110.0% of the labeled amount of metronidazole (C₆H₉N₃O₃).

Prepare Metronidazole Benzoate Compounded Oral Suspension containing 50 mg/mL of metronidazole as follows (see Pharmaceutical Compounding-Nonsterile Preparations (795)).

^a Perrigo, Minneapolis, MN.

Place the Metronidazole Benzoate powder into a suitable mortar. Wet the powder with a small amount of Ora-Blend, and triturate to make a smooth paste. Add the Ora-Blend in small portions almost to volume, and mix thoroughly after each addition. Transfer the contents of the mortar, stepwise and quantitatively, to a calibrated container. Add sufficient Ora-Blend to bring the preparation to final volume. Shake to mix well.

2 ASSAY

PROCEDURE

Solution A: 0.1% (v/v) glacial acetic acid in water

Mobile phase: Acetonitrile and Solution A (40:60). Filter, and degas.

Standard solution: 0.4 mg/mL of metronidazole prepared from USP Metronidazole Benzoate RS in Mobile phase. Mix well until dissolved.

Sample solution: Shake thoroughly each bottle of Oral Suspension. Transfer 0.8 mL of the Oral Suspension into a 100-ml volumetric flask, dilute with Mobile phase to volume, and mix well. 

Chromatographic system

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 316 nm

Column: 4.6-mm x 15-cm; 5-µm packing L1

Column temperature: 30°

Flow rate: 1.0 mL/min

Injection volume: 5 µL

System suitability

Sample: Standard solution

[NOTE-The retention time for metronidazole is about 7.7 min.]

Suitability requirements

Tailing factor: NMT 2.0

Relative standard deviation: NMT 2.0% for replicate injections

Analysis

Samples: Standard solution and Sample solution

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

                         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 metronidazole in the Standard solution (mg/mL) 

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

3 SPECIFIC TESTS

PH (791): 3.6-4.6

4 ADDITIONAL REQUIREMENTS

PACKAGING AND STORAGE: Package in tight, light-resistant containers. Store at 2°-8° or at controlled room temperature.

BEYOND-USE DATE: NMT 90 days after the date on which it was compounded when stored at 2°-8° or controlled room temperature.

LABELING: Label it to indicate that it is to be well-shaken before use, and to state the Beyond-Use Date.

USP REFERENCE STANDARDS (11)

USP Metronidazole Benzoate RS