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.