Clozapine-Associated Leukopenia and Agranulocytosis in Western Cape, South Africa A 3-Year Retrospective Cohort Study

Background Clozapine may cause life-threatening hematological side effects (HSEs). Hematological side effect incidence data from Sub-Saharan Africa are lacking. Furthermore, clozapine reduces cellular immunity, and it is unknown whether clozapine is a risk factor for tuberculosis or whether HIV is a risk factor for developing HSEs. We assessed the incidence of HSEs in South Africans from the Western Cape Province on clozapine, and the secondary objective was to determine the association of HIV and tuberculosis with clozapine exposure. Methods We conducted a 24-week retrospective descriptive study of patients initiated on clozapine between January 2015 and December 2017 using anonymized data from the Provincial Health Data Centre. A control group of patients initiated on risperidone was selected. Results We identified 23,328 patients and included 5213 who had white blood cell monitoring (n = 1047 clozapine, n = 4166 risperidone). The incidence of leukopenia in patients on clozapine was 0.38% (95% confidence interval [CI], 0.01%-0.76%) measured over a 24-week period and was 0.41% in patients on risperidone (95% CI, 0.21%-0.6%) (P = 0.91). The incidence of agranulocytosis in patients on clozapine was 0.19% (95% CI, 0.00%-0.46%) measured over a 24-week period and was 0.24% in patients on risperidone (95% CI, 0.09%-0.39%) (P = 0.266). HIV-infected patients had a 7.46 times increased risk of developing leukopenia (95% CI, 3.37-16.48; P < 0.01). Patients who developed leukopenia had a 6.24 times increased risk of contracting tuberculosis (95% CI, 1.84-21.11; P < 0.01). Conclusions Our incidence of clozapine-induced HSEs was lower than previously reported and not significantly different compared with risperidone. HIV infection was associated with HSEs. Patients with HSEs had an increased risk of developing tuberculosis.

Automated summary

This study assessed the incidence of hematological side effects in South African patients on clozapine and found that HIV infection was associated with these side effects, while patients with HSEs had an increased risk of developing tuberculosis. The incidence of clozapine-induced HSEs was lower than previously reported and not significantly different compared with risperidone.