Minimal effective dose and relapse--double-blind trial: haloperidol decanoate vs. placebo.

Fifty-six chronic schizophrenic patients were randomized into haloperidol decanoate (HD) or placebo groups for 48 weeks of double-blind treatment. The double-blind trial was preceded by a 15-week single-blind run-in period, during which all patients were treated with 60 mg of HD (approximately corresponding to 3.6 mg orally/day) every fourth week (except for the second injection, which was given after 3 weeks). Eight relapses occurred during the run-in period, and seven other patients refused further participation. The remaining 41 patients were then treated double blind, either with HD, 60 mg/4 weeks (18 patients), or with placebo (23 patients). Two patients (11%) in the HD group and 16 (69%) in the placebo group relapsed during the 48-week double-blind period. The plasma concentrations of haloperidol were measured every fourth week in both groups. Steady state was reached after 11 weeks. The mean steady-state level was 6.3 nmol/L. In the placebo group, a 50% decrease in the mean haloperidol plasma concentration was seen 8 weeks after withdrawal of haloperidol. The haloperidol plasma concentration was a predictor of relapse. There was no statistical difference between the treatment groups regarding extrapyramidal symptoms. More biperiden, however, was used in the HD group, while the placebo patients took more sedatives. The results of this study show that the relatively low and fixed dose of 60 mg of HD every fourth week was superior to placebo in preventing relapse in schizophrenia.(ABSTRACT TRUNCATED AT 250 WORDS)