Pharmacokinetics of haloperidol decanoate. A 2-year follow-up.

Plasma haloperidol levels were assayed in 181 chronic schizophrenic inpatients, who were monthly injected intramuscularly with haloperidol decanoate. Steady state levels are reached after the third monthly injection and then remain constant, being associated with a remarkably stable control of the psychotic condition. Between two subsequent injections the haloperidol levels decrease gradually by about half their initial value. The haloperidol plasma levels strongly correlate with the injected doses of the decanoate form. For a single dose of 100 mg haloperidol decanoate monthly the minimal steady state value is about 4 ng/ml.