Treatment-resistant schizophrenia : the relationship between clozapine plasma concentration and clinical outcome

Introduction Clozapine is highly effective in patients with treatment-resistant schizophrenia but, to ensure optimal clinical response it is important to optimize its use and this depends on adequate pharmacological monitoring. Objectives Evaluate the therapeutic response rate according to clozapine plasma concentration. Methods It was a cross-sectional, retrospective and analytical study, carried out over a period of six months, in the F and A psychiatry departments of the Razi hospital in Tunis, including patients followed for treatment-resistant schizophrenia and receiving clozapine. We evaluated the response to clozapine using the Brief Psychiatric Rating Scale (BPRS). Results The average age was 37.7 ± 9.4. The mean age of introduction of clozapine was 31 years and the mean time to its introduction was 9.3 years. Clozapine was administered as a single drug in 85% of cases. The mean dose of clozapine was 373 mg/day. The mean of clozapine plasma concentration was 386.5 ng/ml with a minimum of 89 ng/ml and a maximum of 913 ng/ml. The clinical response rate to clozapine was 25% with a BPRS good response threshold value of less than 35. Patients with clozapine levels above the conventional cut-off of 350 ng/ml (n=34) had a response rate of 34.6%. A response rate of 37% was observed in the group of patients with a clozapine plasma concentration interval of 200-350 ng/ml. There was no statistically significant difference in therapeutic response (p=0186) Conclusions Our study revealed a therapeutic response variation according to plasma clozapine concentration and showed the existence of a non-negligible and effective response rate. Disclosure No significant relationships.