Name: Methenamine
Class: UTI Agent
Mech.: Decomposes at pH £5.5 to NH4+ and formaldehyde (bactericidal).
Absorption: Oral very good, but ¯ pH of stomach decomposes lots of the drug. Enteric-coated tablet solves most of problem.
Distribution: Activated 1° in urine.
Metab.: NH4+ production requires fxning liver for excretion. Kidneys only important if methenamine mandelate or hippurate is used.
Excretion, t½: Excreted in urine. NH4+ reduced requires liver for excretion.
Toxicity/S.E.s: GI distress. Long term = rash, hematuria, albuminuria, painful/frequent micturition.
Utility: Chronic suppression of UTIs.
Special Features: No resistance formation. Orgs which raise urine pH inhibit formaldehyde formation ® ¯ sensitivity.