Lack of effect of methenamine in suppression of, or prophylaxis against, chronic urinary infection

Methenamine is frequently prescribed for patients who have chronic urinary infection to suppress bacterial growth during active infection or to prevent recurrence once an infection has been brought under control. We have examined the effect of methenamine mandelate and ascorbic acid on bacteriuria in para- and quadriplegics from a spinal cord unit. Patients with indwelling urinary catheters and those on a program of intermittent catheterization were included. No suppressive or prophylactic effect of this regimen was observed in any of our patients. Methenamine does not appear to be an effective antimicrobial agent in subjects who have an indwelling urinary catheter or in patients with spinal cord injury who are on intermittent catheterization. Since there appears to be reason to question the efficacy of methenamine in situations in which it is usually prescribed, evidence should be sought for a therapeutic effect in other cases. If no benefit is observed, the drug should not be used.