Drug therapy reviews: methenamine mandelate and methenamine hippurate.

The mechanism of action, spectrum of antimicrobial activity, pharmacokinetics, adverse effects, therapeutic use, and dosage of methenamine hippurate and methenamine mandelate are reviewed. The antimicrobial activity of methenamine depends on its conversion in the urine to formaldehyde. Formaldehyde's spectrum of antibacterial activity encompasses all urinary tract pathogens. Urinary concentrations of formaldehyde vary with pH and urine volume; however, there is no documentation that acdification of the urine enhances methenamine's therapeutic activity. Adverse reactions to methenamine, including gastrointestinal intolerance and skin reactions, are mild and reversible and occur infrequently. Methenamine mandelate and hippurate are effective in the prevention of recurrent urinary tract infections except in patients with Foley catheters or who require intermittent catheterization.