Pharmacokinetic–Pharmacodynamic Modeling of Severity Levels of Extrapyramidal Side Effects With Markov Elements

A major problem in the treatment of schizophrenic patients with current antipsychotic drugs, mainly acting as dopamine-2 receptor antagonists, is the occurrence of side effects such as extrapyramidal symptoms (EPS). Meta-analyses of summary data of EPS occurrence, and receptor occupancies inferred from mean plasma concentrations, have shown the incidence of EPS to rise when receptor occupancy is above ~80%. In this analysis, individual longitudinal EPS data from 2,630 patients participating in one of seven different trials and treated with haloperidol, paliperidone, ziprasidone, olanzapine, JNJ-37822681, or placebo were analyzed using a continuous time probability model with Markov elements. The developed pharmacokinetic–pharmacodynamic model describes the longitudinal changes of spontaneously reported EPS-related adverse events and their severity levels rated by clinicians. Individual steady-state concentrations and occupancy levels were found to be predictors for EPS. The results confirm 80% occupancy as a level of increased EPS occurrence rates, also at the individual level.