Reduced haloperidol plasma concentration and clinical response in acute exacerbations of schizophrenia

Twenty-nine hospitalized patients suffering acute exacerbations of schizophrenia were treated for 2 weeks with fixed daily oral doses of haloperidol prospectively calculated to achieve a haloperidol plasma concentration of either 8–18 ng/ml or 25–35 ng/ml. Reduced haloperidol as well as haloperidol concentrations were assayed to determine if the former enhanced the predictability of response. Week 2 haloperidol plasma concentrations were negatively correlated to clinical response as measured by the percentage change in the BPRS score from baseline (r=–0.43,P<0.05). In contrast, week 2 plasma concentrations of reduced haloperidol, total haloperidol (haloperidol+reduced haloperidol), and reduced haloperidol/haloperidol ratio did not correlate with the change in the BPRS score. Chi-square analysis concluded that patients with ratios greater than one were no less likely to be treatment responders (<25% improvement in BPRS from baseline and week 2 BPRS <55) than those with ratios less than one. Although these data lend additional support to reports of a curvilinear relationship between haloperidol plasma concentration and clinical response, they also suggest that reduced haloperidol plasma concentrations are of no value in predicting treatment response.From the Mental Health Research Center — Major Psychoses, funded in part by NIMH Grant #5 P50 MH43271