Pharmacokinetic protocol for predicting plasma haloperidol concentrations.

The accurate prediction of steady-state plasma haloperidol concentrations was successfully accomplished by obtaining two blood samples following a 20 mg test dose (kinetic method). Prediction of steady-state concentrations on the basis of a mg/kg/day dosage (dose method), although equally precise, generated significantly less information concerning the variance between observed and predicted haloperidol plasma concentrations. Both predictive methods were less precise when the daily doses exceeded 0.47 mg/kg/day. Fifty percent (6/12 patients) of the haloperidol plasma concentrations were underpredicted if this threshold was exceeded. This finding may suggest the possibility of dose-dependent pharmacokinetics with haloperidol in some patients.