Clozapine metabolism rate as a possible index of drug-induced granulocytopenia

Abstract

A possible relationship between haematological adverse reactions and clozapine (CLZ) metabolism rate was studied. Sixteen chronic schizophrenic outpatients (mean age 34.62 years ± 7.56 SD) were treated with CLZ, 75–600 mg/daily for 9 weeks. CLZ and norclozapine (NCLZ) plasma levels were determined weekly, contemporarily with blood cell counts.  CLZ plasma levels ranged from 25 to 1270 ng/ml (mean 266.27 ng/ml ± 197.44 SD), while NCLZ plasma levels ranged from 25 to 1280 ng/ml (mean 169.0 ng/ml ± 127.94 SD). NCLZ/CLZ ratio ranged from 0.13 to 1.72 (mean 0.72 ± 0.28 SD). Leukocyte count ranged from 5.2 to 18.8 10⁹/l (mean 9.37 10⁹/l ± 2.94 SD) and neutrophil count ranged from 1.8 to 13.4 10⁹/l (mean 5.73 ± 2.57 SD). No correlation was found between CLZ dosage and NCLZ plasma levels. Both CLZ and NCLZ plasma levels correlated positively with neutrophil count (CLZ: P = 0.001, r = 0.26; NCLZ: P = 0.01, r = 0.20). The correlation between NCLZ/CLZ plasma level ratio and neutrophil count was significantly negative (P = 0.002, r  = 0.25). These preliminary data suggest that the NCLZ/CLZ ratio, as an index of CLZ metabolism, might be a possible risk factor associated with CLZ treatment.