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ANTIINFECTIVES FOR SYSTEMIC USE › ANTIBACTERIALS FOR SYSTEMIC USE › OTHER ANTIBACTERIALS › Other antibacterials
methenamine
J01XX05
Forms & Strengths
- Methenamine hippurate: 1 g tablets
- Methenamine mandelate: 0.5 g and 1 g enteric-coated tablets
Adult Dosing
- Methenamine hippurate: 1 g orally twice daily (morning and evening)
- Methenamine mandelate: 1 g orally four times daily after meals and at bedtime
Pediatric Dosing
- Children 6-12 years (hippurate): 500 mg to 1 g orally twice daily
- Children 6-12 years (mandelate): 500 mg orally four times daily
- Children under 6 years: Use dosage based on weight and clinical response under specialist guidance
Indications
- Prophylaxis or suppression of frequently recurring urinary tract infections
- Not indicated for acute infections or parenchymal renal infections
Mechanism of Action
- Hydrolyzes in acidic urine (pH <= 5.5) to release formaldehyde, which acts as a nonspecific urinary antiseptic
- Produces bactericidal activity against various Gram-negative and Gram-positive uropathogens
Contraindications
- Renal impairment (severe)
- Hepatic insufficiency (severe)
- Severe dehydration
- Concomitant sulfonamide use (risk of insoluble precipitate formation in urine)
Adverse Reactions
- Nausea and dyspepsia
- Gastric upset and cramps
- Dysuria and urinary frequency
- Skin rashes and pruritus
- Elevated transaminases (rare)
Drug Interactions
- Sulfonamides: May form an insoluble precipitate in acidic urine, increasing crystalluria risk
- Alkalinizing agents (e.g., sodium bicarbonate, acetazolamide, thiazide diuretics): Raise urinary pH, preventing the conversion of methenamine to formaldehyde and reducing efficacy
Curated Content: Needs Vetting Before Put to Clinical Use