Haloperidol plasma levels and dose optimization

Objective: This study was designed to test the practical utility of haloperidol plasma level determinations in the management of schizophrenic patients who show poor initial responses to haloperidol. Method: Inpatients with acute exacerbations of DSM-III schizophrenia (N=66) were randomly assigned to receive fixed haloperidol doses intended to achieve plasma levels of 8-18 ng/ml or of 25-35 ng/ml. Patients whose scores on the Brief Psychiatric Rating Scale (BPRS) failed to improve by at least 30% at the end of 3 weeks were then subject to dose reassignment. Results: Among the patients who completed the fir`st phase of the protocol, 30 had steady-state haloperidol plasma levels of less than 18 ng/ml, and 22 had levels that exceeded 25 ng/ml; 14 had intermediate plasma levels of 18-25 ng/ml. A survival analysis of time to 38% improvement significantly favored the two lower plasma level groups, although side effect ratings did not differ. Of the 30 patients whose BPRS scores failed to improve by 30% after 3 weeks, 11 and five were randomly assigned to receive lower and higher doses, respectively. Those whose dose was lowered experienced significantly more improvement in the subsequent weeks than did those whose dose was increased. Conclusions: Haloperidol plasma levels that substantially exceed 18 ng/ml may be countertherapeutic. In particular, increases in dose beyond this level are not efficacious for patients who have not responded to lower doses.