HALOPERIDOL PLASMA-CONCENTRATIONS IN TAIWANESE PSYCHIATRIC-PATIENTS

Haloperidol and reduced haloperidol are interconverted. The plasma con centrations of these two butyrophenones have been suggested to be impo rtant factors in determining the clinical effect of haloperidol treatm ent. The steady-state plasma concentrations of haloperidol and reduced haloperidol were measured in 322 Taiwanese schizophrenic patients usi ng high performance liquid chromatography. The daily doses of haloperi dol varied from 5 to 200 mg (mean +/- SD, 35.3 haloperidol +/- 34.6 mg ). There was a positive correlation between plasma concentrations and doses, following the equation: haloperidol concentration (ng/mL) = 0.8 8 x dose (mg/day) - 1.66. However, the interpatient variation in halop eridol concentrations was up to ten-fold even in patients receiving th e same dose (20 mg/day, n = 88). The expected values were about 10% to 50% higher than those reported in Caucasian patients. The plasma redu ced haloperidol concentrations were significantly lower than, and corr elated with, those of haloperidol in patients with haloperidol levels lower than 25 ng/mL. However, once haloperidol exceeded 25 ng/mL, redu ced haloperidol levels rapidly elevated and appeared significantly hig her than haloperidol levels. While haloperidol could reach its steady state in about 1 week, reduced haloperidol needed at least 4 weeks to do so. Haloperidol doses of less than 30 mg/day and plasma concentrati ons lower than 25 ng/mL are recommended for most Chinese patients.