Methenamine

Methenamine.svg

Methenamine, also known as hexamethylenetetramine, is a urinary antiseptic used primarily for the treatment and prevention of urinary tract infections (UTIs). It is a prodrug that is converted to formaldehyde in acidic urine, which acts as an antiseptic agent.

Mechanism of Action

Methenamine is a prodrug that is hydrolyzed to formaldehyde and ammonia in acidic environments. The formaldehyde released in the urine acts as a bactericidal agent, effectively killing bacteria in the urinary tract. The effectiveness of methenamine depends on the acidity of the urine, with optimal activity occurring at a pH of 5.5 or lower.

Clinical Uses

Methenamine is used for the prophylaxis and treatment of recurrent UTIs. It is particularly useful in patients who require long-term suppression of bacterial growth in the urinary tract. Methenamine is not effective for acute UTIs and should not be used as a first-line treatment for such infections.

Pharmacokinetics

Methenamine is administered orally and is absorbed from the gastrointestinal tract. It is distributed throughout the body but is primarily excreted unchanged in the urine. The half-life of methenamine is approximately 3 to 4 hours. The drug is most effective when the urine is acidic, and patients may be advised to take ascorbic acid or other urinary acidifiers to maintain an acidic urine pH.

Side Effects

Common side effects of methenamine include gastrointestinal disturbances such as nausea, vomiting, and diarrhea. Rarely, patients may experience allergic reactions, including rash and urticaria. Methenamine should be used with caution in patients with renal impairment or hepatic impairment.

Contraindications

Methenamine is contraindicated in patients with severe renal impairment, severe hepatic impairment, or dehydration. It should not be used in patients with gout or hyperuricemia due to the potential for increased uric acid levels.

Drug Interactions

Methenamine may interact with drugs that alkalinize the urine, such as acetazolamide or sodium bicarbonate, reducing its effectiveness. It may also interact with sulfonamides, increasing the risk of crystalluria and renal damage.

Also see

• Urinary tract infection
• Formaldehyde
• Prodrug
• Urinary antiseptic