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 void ing. We performed a randomized, double-blind, placebo-controlled, cros sover study in eight normal male volunteers (phase I) and in 11 patien ts with documented benign prostatic hypertrophy (phase II) to study th e 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 testi ng was performed with serial threefold dilutions of histamine to asses s efficacy and degree of compliance. Uroflowmetry and urinary symptom assessment were also done. In phase I, after 1 week of terfenadine, me an 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 wa s 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 voidi ng symptom scores. We conclude that the commonly recommended dose of t erfenadine does not significantly alter voiding characteristics in nor mal men or in patients with documented benign prostatic hypertrophy.