Generic Name

Methenamine

Precaution

Patient w/ indwelling urinary catheters; conditions wherein urine acidification is contraindicated or unattainable (e.g. presence of urea-splitting bacteria in the urine). Mild to moderate hepatic impairment. Childn. Pregnancy and lactation. Not intended for use in upper UTI. Monitoring Parameters Monitor urinalysis, urine culture, LFT. Maintain an acidic urine, or give supplemental acidification (e.g. ammonium Cl, ascorbic acid, methionine), if necessary.

Indication

Asymptomatic bacteriuria, Treatment and prophylaxis of chronic, uncomplicated lower urinary-tract infections.

Contra Indication

Hypersensitivity. Gout, metabolic acidosis, severe dehydration. Renal and severe hepatic impairment. Concomitant use w/ sulfonamides or alkalinising agents.

Dose

Oral Asymptomatic bacteriuria, Treatment and prophylaxis of chronic, uncomplicated lower urinary-tract infections. Adult: As methenamine hippurate: 1,000 mg bid. In catheterised patient: 1,000 mg tid. As methenamine mandelate: 1,000 mg 4 times daily. Child: <6 yr As methenamine mandelate: 18 mg/kg 4 times daily; 6-12 yr As methenamine hippurate: 500-1,000 mg bid; As methenamine mandelate: 500 mg 4 times daily; >12 yr: As methenamine hippurate/mandelate: Same as adult dose.

Side Effect

1-10% Dysuria Gastric upset Nausea Rash

Pregnancy Category

Mode of Action

Methenamine is a urinary antibacterial agent. Its action depends on its conversion in acidic urine into formaldehyde, a nonspecific bactericidal agent, that is active against both gram+ve and gram-ve bacteria.

Interaction

Acetazolamide may inhibit conversion of methenamine into formaldehyde. Potentially Fatal: Risk of crystalluria when given w/ sulfonamides (e.g. sulfamethizole) or urinary alkalinising agents (e.g. potassium citrate).

Pregnancy Category Note

Pregnancy Category: C Lactation: excreted in breast milk; no adverse effects documented

Adult Dose

Oral Asymptomatic bacteriuria, Treatment and prophylaxis of chronic, uncomplicated lower urinary-tract infections. Adult: As methenamine hippurate: 1,000 mg bid. In catheterised patient: 1,000 mg tid. As methenamine mandelate: 1,000 mg 4 times daily.

Child Dose

Oral Asymptomatic bacteriuria, Treatment and prophylaxis of chronic, uncomplicated lower urinary-tract infections. Child: <6 yr As methenamine mandelate: 18 mg/kg 4 times daily; 6-12 yr As methenamine hippurate: 500-1,000 mg bid; As methenamine mandelate: 500 mg 4 times daily; >12 yr: As methenamine hippurate: 1,000 mg bid. In catheterised patient: 1,000 mg tid. As methenamine mandelate: 1,000 mg 4 times daily.

Renal Dose

Renal impairment: Contraindicated.

Administration

N/A