Biperiden effects and plasma levels in volunteers

The pharmacokinetics of biperiden was studied and compared with pharmacodynamics (pupil size, accommodation, self-rating mood scale) in 6 healthy volunteers. A single-blind cross-over design was employed with placebo and biperiden (4 mg as commercially available tablets). After a lag time of 0.5 h, biperiden was rapidly absorbed with a half-life of 0.3 h, plasma peak levels of 5 ng/ml being reached after 1.5 h. Biperiden showed good tissue penetration (distribution half-life 0.6 h; ratio of total to central distribution volume 9.6), the terminal half-life time of plasma concentration was 18 h, and the oral clearance was 146 l/h. The pharmacodynamic maximum lagged behind the plasma peak concentration by 1 (self-rating) to 4 h (accommodation).