Pharmacokinetic and pharmacodynamic studies following the intravenous and oral administration of the antiparkinsonian drug biperiden to normal subjects

The pharmacokinetics and pharmacodynamics (changes in pupil size and salivary flow) of biperiden following a single oral and intravenous dose were investigated in six normal subjects. After the injection plasma concentrations declined biphasically, with half-times of 1.5 h for the rapid phase and 24 h for the terminal phase. Clearance and apparent volume of distribution were high (12 ml·min^-1·kg^-1 and 24 l·kg^-1 respectively). Absorption was rapid but the systemic availability was incomplete (33%), probably due to first-pass metabolism. Central nervous system (CNS) adverse effects and changes in pupil size were observed after both routes of administration while salivary flow was affected only by the injection.