Do oral antimuscarinic drugs carry an increased risk of acute urinary retention?

Purpose: We determined whether men treated with oral antimuscarinics are at increased risk for acute urinary retention.

Materials And Methods: In this population based, retrospective cohort study using a nested case-control design we analyzed data from a large primary care database containing patient information entered by general practitioners in the United Kingdom. Our study cohort comprised men 20 to 84 years old. Cases of acute urinary retention were identified by reviewing diagnostic codes and were confirmed in a random sample through questionnaires sent to the treating physician.

Results: The overall incidence of acute urinary retention in the study cohort (1,844) was 1.0 per 1,000 person-years, with the incidence rate increasing with age. The first 30 days (early treatment) of antimuscarinic use was associated with a relative risk of acute urinary retention of 8.3 (95% CI 4.8-14.2) and with longer term use (more than 30 days) the relative risk was 2.0 (95% CI 1.2-3.1). The relative risk of acute urinary retention was similar for low/medium and high antimuscarinic doses (relative risk 2.8 vs 3.0, 95% CI 2.1-3.8 and 1.3-6.8, respectively). The relative risk of acute urinary retention was highest during early treatment for a urogenital indication (relative risk 14.2, 95% CI 6.8-29.6). The risk of acute urinary retention was not increased when antimuscarinics were used as antispasmodics or for drug induced parkinsonism.

Conclusions: Men prescribed antimuscarinics, particularly for a urogenital condition, should be closely monitored during the first 30 days of treatment for signs or symptoms of urinary retention.