Effect of terfenadine on urination.

Anticholinergic side effects of commonly used antihistamines are known to aggravate voiding difficulties in older men with benign prostatic hypertrophy. Newer antihistamines, such as terfenadine (Seldane), with less anticholinergic side effects may not have such an effect on voiding. We performed a randomized, double-blind, placebo-controlled, crossover study in eight normal male volunteers (phase I) and in 11 patients with documented benign prostatic hypertrophy (phase II) to study the effect of terfenadine on voiding. Subjects received either 60 mg of terfenadine or an identical placebo twice daily for 1 week each. After a 1-week washout period, they were crossed over to receive the other drug. Evaluation took place on days 0, 7, 14, and 21. Prick skin testing was performed with serial threefold dilutions of histamine to assess efficacy and degree of compliance. Uroflowmetry and urinary symptom assessment were also done. In phase I, after 1 week of terfenadine, mean skin test suppression was 83.8% compared with -0.5% with placebo (P < .01). Urinary peak flow increased 10.4% on terfenadine and 9.7% on placebo (P = NS). In phase II, the mean prick skin test suppression was 87.8% compared with 12.0% for placebo (P < .002). Urinary peak flow was decreased 0.1% from baseline on terfenadine and increased by 18.7% for placebo (P = NS). None of the subjects noted alterations in voiding symptom scores. We conclude that the commonly recommended dose of terfenadine does not significantly alter voiding characteristics in normal men or in patients with documented benign prostatic hypertrophy.