A practical loading dose method for converting schizophrenic patients from oral to depot haloperidol therapy

Abstract

Background: Haloperidol decanoate is a long-acting depot antipsychotic agent used for the treatment of schizophrenic patients. The decanoate formulation was developed to treat schizophrenics who have a history of noncompliance with oral medication. Studies of techniques to convert from oral to depot therapy have not utilized the pharmacokinetics of the decanoate formulation. This study is a prospective evaluation for converting patients from oral to depot treatment.

Method: Twenty-one patients meeting DSM-III-R criteria for schizophrenia participated in the study. Patients were treated with oral haloperidol for 6 weeks and then were switched to decanoate. Haloperidol decanoate 100 mg was administered on a weekly basis for the first 4 weeks. Afterward, injection intervals were increased to every 2 weeks and then to every 4 weeks. Plasma haloperidol concentrations were obtained prior to the next injection and assayed by HPLC with electrochemical detection. Patients were monitored by the psychiatrists and nursing staff for symptoms of clinical deterioration.

Results: All patients completed the conversion trial during the first 4 weeks without any problems or adverse side effects. By the third week, mean plasma haloperidol concentrations from the decanoate injections were comparable with those of the 10-mg oral haloperidol treatment (7.95 +/- 4.94 ng/mL vs. 7.79 +/- 4.79 ng/mL). Steady-state conditions for the decanoate therapy were achieved by the fourth week.

Conclusion: These findings suggest that schizophrenic patients can be easily converted from oral to depot therapy without problems. Further studies with haloperidol decanoate and its conversion from oral treatment utilizing plasma concentrations are needed.