Generic
Methenamine
3 brands available in the market
At a glance
Methenamine is used for the treatment and prophylaxis of chronic, uncomplicated lower urinary tract infections. It acts by converting to formaldehyde in acidic urine, exhibiting bactericidal activity.
Description
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-positive and gram-negative bacteria.
Indications
- Asymptomatic bacteriuria
- Treatment and prophylaxis of chronic, uncomplicated lower urinary tract infections
- Long-term therapy for prevention of recurrent cystitis
- Suppression of urinary infection in patients with indwelling catheters
- Prophylaxis against infection during instrumental procedures
Therapeutic class
Other Genito-urinary Preparations
Pharmacological class
Urinary Antibacterial Agent
Pharmacology
Methenamine converts to formaldehyde in acidic urine, which exhibits bactericidal activity against both gram-positive and gram-negative bacteria.
Mechanism of action
Kills bacteria by converting to formaldehyde in acidic urine.
Dosage
Adult Dose (Oral):
- Methenamine hippurate: 1000 mg twice daily
- Catheterized patient: 1000 mg three times daily
- Methenamine mandelate: 1000 mg 4 times daily
Children (6-12 years): 0.5-1 g twice daily; >12 years: adult dose
Administration
- Take oral tablets with water
- Restrict alkalinizing foods and medications to maintain acidic urine
- Supplemental acidification with ammonium chloride, ascorbic acid, methionine if needed
Missed dose
Not generally applicable (regular use); consult doctor if needed.
Side effects
Common Side Effects (1-10%):
- Dysuria
- Gastric upset
- Nausea
- Rash
Precautions & warnings
- Caution in patients with indwelling urinary catheters
- Caution in conditions where urine acidification is contraindicated or unattainable (e.g., urea-splitting bacteria)
- Not intended for use in upper UTI
- Monitor urinalysis, urine culture, LFT
- Maintain acidic urine
Contraindications
- Hypersensitivity
- Gout, metabolic acidosis, severe dehydration
- Renal and severe hepatic impairment
- Concomitant use with sulfonamides or alkalinizing agents
Drug interactions
- Acetazolamide may inhibit conversion of methenamine to formaldehyde
- Risk of crystalluria with sulfonamides (sulfamethizole) or urinary alkalinizing agents (potassium citrate) - potentially fatal
Food interactions
No food interactions known.
Use in pregnancy
Use in Pregnancy: Methenamine may be unsafe during pregnancy (Category C); animal studies have shown effects on fetus; use only if benefits outweigh risks.
Pregnancy Category: C — always consult a doctor before taking during pregnancy.
Use in lactation
Use in Lactation: Methenamine is excreted in breast milk; no adverse effects documented; caution is advised.
Pediatric use
Pediatric dose established for children under 6 years (mandelate form); doses established for children 6-12 years.
Geriatric use
Elderly may require dose adjustment (based on renal function).
Renal / hepatic impairment
Renal Impairment: Contraindicated in renal insufficiency.
Hepatic Impairment: Contraindicated in severe hepatic insufficiency; caution in mild-moderate hepatic impairment.
Overdose effects
Overdose: induce vomiting or gastric lavage, activated charcoal; increase fluid intake.
Storage conditions
Store below 30°C, away from light and moisture; keep out of reach of children.
Chemical structure
Methenamine