The usefulness of monitored therapy using Clozapine concentration in the blood serum for determining drug dose in Polish schizophrenic patients

Background: The aim of the study is to evaluate the advisability of systematic monitoring of clozapine (CLO) concentration in serum during treatment of schizophrenia in Polish psychiatric patients. Method: The concentration of CLO and its metabolites: norclozapine (NCLO) and clozapine N-oxide (CLO-NO) in serum obtained from 107 patients suffering from schizophrenia was determined by high performance liquid chromatography (HPLC) method. There were two groups of patients. In the first group of patients (n = 95) the concentration of drug and its metabolites was determined by one-time testing. Correlations were tested using the test statistics. In the second group of patients (n = 12), 51 samples of serum were provided by the same patient in different time spans (from 6 days to 14 months after the beginning of the treatment). Results: Concentrations of CLO and its metabolites in blood serum do not always show a linear dependence on the applied dose for individual patients. Conclusion: The high volatility of CLO concentrations in blood serum of patients treated with identical doses of the drug confirmed the validity of the monitored therapy.