Pharmacokinetics of chlorprothixene after single intravenous and oral administration of three galenic preparations.

The absolute and relative bioavailability of chlorprothixene (CAS 113-59-7, Truxal) was studied in eight healthy male volunteers with three different formulations: solution, suspension and coated tablet. An intravenous infusion and an oral aqueous solution served as references. Single doses of 100 mg were administered in a randomized complete-block design with washout periods of two weeks. Serum concentrations of chlorprothixene were assayed using a high-performance liquid chromatographic method with electrochemical detection. After a 1-h infusion period the maximum serum concentration (Cmax) of chlorprothixene was 430 +/- 81 ng/ml (mean +/- S.D.) and subsequently decreased with a terminal elimination half-life (t1/2) of 25.8 +/- 13.6 h. The total serum clearance (Cl) and the apparent volume of distribution at steady state (Vss) were 867 +/- 167 ml/min and 1035 +/- 356 l, respectively. The profiles of the chlorprothixene serum concentration vs. time and the resulting pharmacokinetic parameters were similar for all orally administered formulations. The absolute oral bioavailability of 17% of the solution indicated a marked presystemic metabolism. The bioavailability of chlorprothixene relative to the oral solution was 56.4% with the coated tablet and 67.7% with the suspension. All pharmacokinetic parameters showed wide inter-subject variations, partly attributable to the respective formulation.