METHENAMINE MANDELATE

DRUG INTERACTIONS Formaldehyde and sulfamethizole form an insoluble precipitate in acid urine; therefore, methenamine mandelate, USP should not be administered concurrently with sulfamethizole.

INDICATIONS AND USAGE Methenamine mandelate is indicated for the suppression or elimination of bacteriuria associated with pyelonephritis, cystitis, and other chronic urinary tract infections; also those neurologic diseases leading to an infected residual urine. When used as recommended, methenamine mandelate is particularly suitable for long-term therapy because of its safety and because resistance to the nonspecific bactericidal action of formaldehyde does not develop. Pathogens resistant to other antibacterial agents may respond to methenamine mandelate because of the nonspecific effect of formaldehyde formed in an acid urine. Prophylactic Use Rationale: Urine is a good culture medium for many urinary pathogens. Inoculation by a few organisms (relapse or reinfection) may lead to bacteriuria in susceptible individuals. Thus, the rationale of management in recurring urinary tract infection (bacteriuria) is to change the urine from a growth-supporting to a growth-inhibiting medium. There is a growing body of evidence that long-term administration of methenamine mandelate can prevent the recurrence of bacteriuria in patients with chronic pyelonephritis. Therapeutic Use Rationale : Methenamine mandelate helps to sterilize the urine, and in some situations in which underlying pathologic conditions prevent sterilization by any means, it can help to suppress the bacteriuria. Methenamine mandelate should not be used alone for acute infections with parenchymal involvement causing systemic symptoms such as chills and fever. A thorough diagnostic investigation as a part of the overall management of the urinary tract infection should accompany the use of methenamine mandelate.

DOSAGE AND ADMINISTRATION The average adult dose is 4 g daily given as 2 teaspoon after each meal and at bedtime. Children 6 to 12 should receive half the adult dose, and children under 6 years of age should receive 250 mg per 30 lb body weight, four times daily. Since an acid urine is essential for antibacterial activity, with maximum efficacy occurring at pH 5.5 or below, restriction of alkalinizing foods and medication is thus desirable. If testing of urine pH reveals the need, supplemental acidification should be given.

ADVERSE REACTIONS Gastrointestinal disturbances (nausea, stomach upset), generalized skin rash, dysuria, painful or difficult urination may occur occasionally with the use of methenamine preparations. Microscopic and rarely, gross hematuria have been described.