Perphenazine decanoate and cis(Z)-flupentixol decanoate in maintenance treatment of schizophrenic outpatients. Serum levels at the minimum effective dose

Two groups of schizophrenic outpatients were treated with perphenazine decanoate (N = 20) and cis(z)-flupentixol decanoate (N = 24) respectively. Every 3 months the dose was gradually reduced until symptoms appeared that were suggestive of a prodromal phase of a psychotic episode. A slightly higher dose was then promptly reinstituted (the minimum effective dose). At each dose level, two blood samples were drawn for determination of serum concentration. The mean minimum effective dose of perphenazine decanoate was 99.3 mg/2 weeks (range 21.6-270.5), while the mean minimum effective dose of cis(z)-flupentixol decanoate was 60 mg/2 weeks (range 20-250). The corresponding mean serum level of perphenazine decanoate was 7.3 nmol/l (range 2.0-18.1) and of cis(z)-flupentixol decanoate 7.8 nmol/l (range 1.2-37.0). There was a significant correlation between the administered doses and the corresponding serum levels for both drugs (r = 0.87, P less than 0.01). A weak positive correlation was found between serum levels at the minimum effective dose and symptom intensity (BPRS total score) (r = 0.53, P less than 0.02) for perphenazine, but not cis(z)-flupentixol. No correlation was found between serum levels and side effects or length of neuroleptic treatment. It is concluded that the serum drug concentrations corresponding to the lowest effective dose are so variable that routine serum level monitoring may be of limited value in the long-term maintenance treatment of schizophrenia.