Preventive effect of methenamine in women with recurrent urinary tract infections – a case–control study

BACKGROUND: Urinary tract infection (UTI) is the most common bacterial infection in women. In Norwegian general practice, methenamine has been prescribed for many years as long-term prevention and accounted for 20% of the total antibiotic prescribing in 2015, as measured in defined daily dosages (DDDs). The efficacy of methenamine is unknown. If shown to be effective, this drug may become an important preventive against UTI. OBJECTIVE: To examine whether methenamine is preventive against recurrent UTI in women. DESIGN: Data for all antibiotics used for UTIs dispensed from all pharmacies from 2005 to 2015 were collected from the Norwegian prescription database (NorPD). SUBJECTS: Women aged ≥ 40 years with recurrent UTI, defined as ≥3 courses of UTI antibiotic/year, were included. MAIN OUTCOME MEASURES: Patients using methenamine (cases) and those not using methenamine (controls) were compared. The numbers of UTI prescriptions during the 2 years before and after inclusion were analysed. Results: The yearly prevalence for recurrent UTI was 2.4% in women ≥ 40 years. The change in antibiotic use from 2 years before to 2 years after inclusion in the study differed significantly between groups: 44.6 and 34.9% reductions in the number of antibiotic prescriptions for UTI in the methenamine and control groups, respectively. The decrease in UTI antibiotic prescriptions (58.9%) was greater in patients with a higher consumption of antibiotics before starting methenamine. CONCLUSIONS: KEY POINTS: Methenamine has been used for many years for prevention of recurrent UTI, but no studies have demonstrated a significant preventive effect of long time use. This study shows that methenamine seems to be effective for prevention in patients having recurrent UTI over 2 years or more. The effect seems to be larger in patients with a high number of UTIs over 2 years.