Intramuscular haloperidol decanoate for neuroleptic maintenance therapy. Efficacy, dosage schedule and plasma levels. An open multicenter study.

Thirty-eight hospitalized chronic psychotic patients were injected (i.m.) every 4 weeks with haloperidol decanoate using different dosage schedules which were calculated from the previously prescribed daily oral dose of haloperidol multiplied by a factor of 30, 20 or 10. The 20-fold schedule appeared to be adequate in most of the patients. All patients were well stabilized on their optimal dose schedule and several symptoms improved even further during treatment. No increase of extrapyramidal or other side-effects was reported in any of the patients. Antiparkinson medication could be omitted in 37 patients without problems. There was neither pain nor irritation at the site of injection. Plasma levels of haloperidol reaching a steady state after the second injection of haloperidol decanoate were about two times higher than during the previous oral treatment with haloperidol. No accumulation was observed. Haloperidol decanoate injected every 4 weeks proved to be as safe and therapeutically reliable as orally administered haloperidol.