Methenamine Hippurate

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

Methenamine Hippurate, dried under vacuum at 60° for 1 h, contains NLT 95.5% and NMT 102.0% of methenamine hippurate (C₆H₁₂N₄ · C₉H₉NO₃), and contains NLT 54.0% and NMT 58.0% of hippuric acid (C₉H₉NO₁₀).

2 IDENTIFICATION

Change to read:

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

3 ASSAY

Procedure

Sample solution: Dissolve 700 mg of Methenamine Hippurate in 50 mL of glacial acetic acid.

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N perchloric acid VS

Endpoint detection: Potentiometric

Analysis: Titrate with Titrant. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 31.94 mg of methenamine hippurate (C₆H₁₂N₄ · C₉H₉NO₃).

Acceptance criteria: 95.5%–102.0% on the previously dried basis

4 OTHER COMPONENTS

Content of Hippuric Acid

Sample solution: Transfer 1 g to a 250-mL conical flask, and add 50 mL of water. When the solution is complete, add phenolphthalein TS.

Titrimetric system

Mode: Direct titration

Titrant: 0.1 N sodium hydroxide VS

Endpoint detection: Visual

Analysis: Titrate with Titrant. Each mL of 0.1 N sodium hydroxide is equivalent to 17.92 mg of hippuric acid (C₉H₉NO₁₀).

Acceptance criteria: 54.0%–58.0%

5 IMPURITIES

Residue on Ignition 〈281〉: NMT 0.1%

Sulfate

Sample solution: 200 mg in 10 mL of water

Analysis: Add 5 drops of 3 N hydrochloric acid and 5 drops of barium chloride TS.

Acceptance criteria: No turbidity appears within 1 min.

6 SPECIFIC TESTS

Loss on Drying 〈731〉

Analysis: Dry under vacuum at 60° for 1 h.

Acceptance criteria: NMT 1.0%

7 ADDITIONAL REQUIREMENTS

Packaging and Storage: Preserve in well-closed containers.

USP Reference Standards 〈11〉

USP Methenamine Hippurate RS