[Absolute bioavailability of chlorpromazine, promazine and promethazine]

The absolute bioavailability of the three phenothiazine neuroleptics, promazine (Sinophenin, CAS 58-40-2), chlorpromazine (Propaphenin, CAS 50-53-3) and promethazine (Prothazin, CAS 60-87-7) was tested in three single-dose cross-over studies. In each trial 12 to 14 healthy volunteers were enrolled. The single doses for promazine, promethazine and chlorpromazine were 100, 75 and 150 mg (orally) and 20, 50 and 50 mg (intravenously), resp. The serum concentrations of the three neuroleptics were measured by means of a selective HPLC-method. the distribution-free confidence intervals for the absolute bioavailability of the three phenothiazines were within 10.5 to 24.7% for chlorpromazine, 7.8 to 24.9% for promazine and 12.3 to 40% for promethazine. Promazine and chlorpromazine are pharmacokinetically very similar and differ substantially from promethazine.