A multidose study of haloperidol decanoate in the maintenance treatment of schizophrenia

Maintenance medication is critical in the prevention of psychotic relapse and rehospitalization among patients with schizophrenia. Given potential adverse effects, identification of the minimum effective dose is clinically important.

A multicenter, double-blind study was conducted to determine rates of symptomatic exacerbation and adverse effects in 105 outpatients with schizophrenia randomly assigned to four different fixed doses of haloperidol decanoate and treated for 1 year or until relapse. The doses used were 25, 50, 100, and 200 mg given intramuscularly once per month.

Rates of symptomatic exacerbation were 15% in the 200-mg group, 23% with 100 mg, 25% with 50 mg, and 60% with 25 mg. No significant differences in outcome were found between the groups treated with 200, 100, and 50 mg. Among the patients who completed the trial with no symptomatic exacerbation, there were no differences between dose groups on measures of psychopathology at the final rating point.

The results of this study suggest that the 200-mg/month dose of haloperidol decanoate is associated with the lowest rate of symptomatic exacerbation (15%) with minimal increased risk of adverse effects or subjective discomfort in comparison to 100 or 50 mg. At the same time, the rates of worsening with 100 mg (23%) and 50 mg (25%) were not significantly greater than that seen with 200 mg. These results provide some guidance as to effective dose ranges of haloperidol decanoate.