[Study of residual levels of delayed-action neuroleptics]

Pharmacokinetics of the depot antipsychotics are unclear and mainly depend on releasing from the depot site (according to a "flip-flop" model). Few data are available on residual plasma concentrations of those drugs. We have practiced 38 blood determinations among 15 patients treated by long-acting neuroleptics (10 by fluphenazine decanoate, 4 by flupentixol decanoate and 1 by pipotiazine palmitate). Radio Receptor Assay method was used (based on competition for dopamine receptors binding), with results expressed as chlorpromazine equivalents. They showed; a wide interindividual variability; considering each subject, intraindividual variability is attenuated; blood measurements are mainly higher than therapeutic ranges (especially for patients on fluphenazine decanoate). Those results might involve that some patients are overdosed, but other studies are needed in this way.