[The effect of serum monitoring on concentration of perphenazine and zuclopenthixole].

The effect of therapeutic drug monitoring (TDM), including pharmacokinetic guidance, was examined in 994 psychiatric patients treated with perphenazine (Trilafon) or zuclopentixol (Cisordinol). Before monitoring of the serum level, half of the serum concentrations from patients given perphenazine tablets (466 patients) was below the therapeutic level, and about one third was above. For perphenazine depot (208 patients), almost no patients had a serum concentration below the therapeutic level whereas 40% had concentrations above. For zuclopentixol tablets (231 patienter) and zuclopentixol depot (163 patients), about 60% of the patients had concentrations above the therapeutic level. For all four groups, it was found that slightly more than half of the patients with serum concentrations outside the therapeutic level was reexamined. The dosage was changed in most of these patients (80-90%) in order to bring the concentration within the therapeutic level. Half of those in whom the dose was changed obtained concentrations within the therapeutic level. It is concluded that since the recommendations for changes of the dosage is followed to a wide extent, the therapeutic drug monitoring service does influence the treatment significantly.