Prevention of recurrent acute cystitis by methenamine hippurate: double blind controlled crossover long term study

In a randomised, double blind, long term, crossover study 1 g twice daily of methenamine hippurate was compared with placebo for its preventive effect on recurrent attacks of acute cystitis. Methenamine hippurate and placebo were interchanged every six months for two years. During one of the years patients took 250 ml extra fluid every morning and evening. Out of 21 enrolled patients, 14 completed the first year and 13 both years of treatment, which permitted the evaluation of 27 patient years. There were 52 episodes of acute cystitis caused by reinfection: 41 occurred during placebo treatment and only 11 during the methenamine hippurate regimen (p less than 0.01). Extra fluid intake did not reduce the incidence of acute cystitis, nor did it reduce the effect of methenamine hippurate. Methenamine hippurate is an effective prophylactic agent against recurrent acute cystitis and has the advantage of not inducing cross resistance to conventional antibiotics.