Interindividual variation in serum zuclopenthixol and perphenazine concentrations in orally treated patients

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Abstract
The interindividual variation of the serum concentrations of orally administered zuclopen thixol perphenazine was investigated to evaluate the possible advantages of therapeutic drug monitoring in the initial treatment of acute psychosis. In 94 patients given 20 mg of zuclopenthixol daily under routine conditions, the mean serum concentration was 24.2 nmol/1 (range, 0–80 nmol/1), and the coefficient of variation (CV) was 52%. In 10% of the patients the values were below 10 nmol/1, whereas 26% had values above 30 nmol/1. In 154 patients treated orally with 16 mg perphenazine daily, the mean serum concentration was 2.0 nmol/1 (range, 0–20 nmol/1), and the CV 150%. It is recommended that the serum concentrations be determined during steady state 1 week after start of the treatment, to disclose insufficiently low or unnecessarily high serum concentrations.