INTERINDIVIDUAL VARIATION IN SERUM ZUCLOPENTHIXOL AND PERPHENAZINE CONCENTRATIONS IN ORALLY TREATED PATIENTS

The interindividual variation of the serum concentrations of orally ad ministered zuclopenthixol perphenazine was investigated to evaluate th e possible advantages of therapeutic drug monitoring in the initial tr eatment of acute psychosis. In 94 patients given 20 mg of zuclopenthix ol daily under routine conditions, the mean serum concentration was 24 .2 nmol/l (range, 0-80 nmol/l), and the coefficient of variation (CV) was 52%. In 10% of the patients the values were below 10 nmol/l, where as 26% had values above 30 nmol/l. In 154 patients treated orally with 16 mg perphenazine daily, the mean serum concentration was 2.0 nmol/l (range, 0-20 nmol/l), and the CV 150%. It is recommended that the ser um concentrations be determined during steady state 1 week after start of the treatment, to disclose insufficiently low or unnecessarily hig h serum concentrations.