STEADY-STATE PLASMA-LEVEL PREDICTION FOR HALOPERIDOL FROM A SINGLE TEST DOSE

Due to large interindividual variabilities in kinetics of haloperidol (HPDL), empirically adjusting the dose to achieve steady-state plasma levels (C(ss)) is a time consuming process. We report a method to individualize doses to achieve the desired C(ss) from the observed plasma level 24 hours after a single test dose. Twenty-eight acutely psychotic patients, after up to 2 weeks of inhospital drug washout, received a 15-mg oral "test" dose of HPDL and 24- and 48-hour plasma levels were measured. They were then randomly assigned to empirically determined doses of HPDL (2, 4, or 10 mg b.i.d.) to achieve a low, medium, or high C(ss). The 24-hour plasma level after the test dose, the final C(ss), and the dose required to achieve that C(ss) were analyzed by a linear regression model. The log C(ss) in terms of the log dose revealed a strong linear relationship (R2 = .78, n = 28), which was further improved by the addition of the 24-hour log plasma level (R2 = .87).