A clinical trial comparing intramuscular haloperidol decanoate and oral haloperidol in chronic schizophrenic patients: efficacy, safety, and dosage equivalence.

Thirty patients with chronic schizophrenia received oral haloperidol and haloperidol decanoate in a two-phase open study. In the first phase, patients were stabilized on haloperidol tablets for 2 weeks, then maintained on a constant daily dose for 2 more weeks. They were then switched to haloperidol decanoate for the second phase. Patients were first stabilized on a monthly dose of haloperidol decanoate and then received this dose for 5 consecutive months. Haloperidol decanoate, administered in monthly injections at 9.4 to 15 times the daily oral dose, was at least as efficacious as oral haloperidol in controlling the symptoms of schizophrenia. There were no serious adverse reactions to either drug. Blood samples were taken from 22 patients during both the oral and the decanoate phases and analyzed for steady state haloperidol concentrations. These determinations demonstrate that the release of haloperidol with the decanoate form is sustained throughout the 4-week dosing interval. Lower plasma drug concentrations were observed during decanoate treatment than during oral treatment. Despite these lower plasma concentrations, patients remained stable on both drug regimens. This finding suggests that haloperidol decanoate injected every 4 weeks can provide control of psychotic symptoms at least as effectively as daily oral haloperidol.