Methenamine Hippurate

What it is and how it works

ACTIONS Microbiology: Methenamine hippurate tablets has antibacterial activity because the methenamine component is hydrolyzed to formaldehyde in acid urine. Hippuric acid, the other component, has some antibacterial activity and also acts to keep the urine acid. The drug is generally active against E. coli , enterococci and staphylococci. Enterobacter aerogenes is generally resistant. The urine must be kept sufficiently acid for urea-splitting organisms such as Proteus and Pseudomonas to be inhibited.

Indications

INDICATIONS Methenamine hippurate tablets, USP is indicated for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary. This drug should only be used after eradication of the infection by other appropriate antimicrobial agents. To reduce the development of drug-resistant bacteria and maintain the effectiveness of methenamine hippurate tablets, USP and other antibacterial drugs, methenamine hippurate tablets, USP should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

Dosage and administration (summary)

DOSAGE AND ADMINISTRATION 1 tablet (1.0 g) twice daily (morning and night) for adults and pediatric patients over 12 years of age. 1/2 to 1 tablet (0.5 to 1 g) twice daily (morning and night) for pediatric patients 6 to 12 years of age. Since the antibacterial activity of methenamine hippurate tablets, USP is greater in acid urine, restriction of alkalinizing foods and medications is desirable. If necessary, as indicated by urinary pH and clinical response, supplemental acidification of the urine should be instituted. The efficacy of therapy should be monitored by repeated urine cultures.

Contraindications

CONTRAINDICATIONS Methenamine hippurate tablets are contraindicated in patients with renal insufficiency, severe hepatic insufficiency, or severe dehydration. Methenamine preparations should not be given to patients taking sulfonamides because some sulfonamides may form an insoluble precipitate with formaldehyde in the urine.

Warnings and precautions

WARNING Large doses of methenamine (8 grams daily for 3 to 4 weeks) have caused bladder irritation, painful and frequent micturition, albuminuria, and gross hematuria.

Storage and supply

HOW SUPPLIED Methenamine Hippurate Tablets USP, 1 g are white to off-white capsule shaped tablet, debossed with “L” and “59” on one side and break line (functional) on other side.

Source: Methenamine Hippurate (Methenamine Hippurate) — US FDA prescribing information, 2026-02-03, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.