Comparison of central and peripheral pharmacologic effects of biperiden and trihexyphenidyl in human volunteers

In this double-blind, randomized study, indices of central (memory, sedatio n) and peripheral (salivation, ratio of R-R interval on electrocardiogram) muscarinic function were evaluated in 14 healthy volunteers who received tr ihexyphenidyl, biperiden, and placebo. Additionally, serum drug levels were obtained 2 hours after oral administration. AU subjects participated in th ree study sessions. During each session, subjects received two doses of bip eriden (4 mg), trihexyphenidyl (5 mg), or placebo, and four series of tests were administered, The tests included the determination of cardiac respons e to standing (R-R ratio), mouth salivation, finger-tapping speed, digit sp an (forward and backward), a selective reminding task, and visual analog sc ales (VAS), On the VAS, subjects rated biperiden as significantly more seda ting than either trihexyphenidyl or placebo, and both biperiden and trihexy phenidyl were associated with more dizziness than was placebo, Saliva produ ction was significantly reduced by both trihexyphenidyl and biperiden compa red with placebo. Digit span performance was significantly decreased in onl y the backward direction. The selective reminding task revealed highly sign ificant decrements in the number of words recalled and consistent long-term retrieval after both biperiden and trihexyphenidyl, Delayed recall was sig nificantly decreased by both active drugs. Both trihexyphenidyl and biperid en caused a significant increase in the R-R ratio comparison with placebo. With the exception of the VAS measurement of sedation, the effects caused b y biperiden and trihexyphenidyl did not differ, The results of this study d o not support the hypothesis that the side effect profile of biperiden is s ignificantly different from that of trihexyphenidyl.