Clinical implications of determination of plasma haloperidol levels

The aim of this study was to analyze the clinical utility of monitoring plasma levels, since the utility of monitoring is not yet well established. After a washout period, 30 schizophrenic patients were given fixed doses of haloperidol for 3 weeks. A U-shaped second-grade polynomic relationship (R = 0.69) was found between steady state of haloperidol and percentage improvement in total score on the Brief Psychiatric Rating Scale. The interval of effective concentrations was between 12 and 59 ng/ml. Fourteen of the 15 patients who had a steady state of haloperidol within that therapeutic interval were responders: only 5 out of the 15 patients below the therapeutic interval were responders. None of the 5 patients who had concentrations below 8 ng/ml was a responder. Furthermore, responder patients showed a steady-state level of haloperidol significantly higher than that of nonresponders. These data suggest that plasma levels of haloperidol are predictors of therapeutic response in schizophrenic disorders.