Prevalence and predictors of QTc prolongation in patients seen in a clozapine clinic in a real-world setting in Australia

Background: Many antipsychotic drugs have been associated with QTc prolongation, which is a risk factor for sudden death. We studied the prevalence and predictors of QTc prolongation in treatment-resistant schizophrenia patients who were receiving clozapine in a real-world setting. Methods: Data were extracted from the records of all schizophrenia patients aged 18-65 years, enrolled in a clozapine clinic in metropolitan Australia during October 2020 to April 2022, for whom ECG data were available. Results: There were 104 eligible patients. The mean age of the sample was 42 years. The sample was 56 % male. About a third of patients were receiving antipsychotic and antidepressant drugs in addition to clozapine. The mean (standard deviation) QTc was 437.0 (24.8) ms in men and 445.8 (28.5) ms in women. QTc prolongation was present in 36.5 % of the sample. In univariate analysis, higher heart rate and higher clozapine levels were significantly associated with QTc prolongation; in multivariable logistic regression analysis, nonsignificant statistical trends were observed for male sex, higher heart rate, and higher serum clozapine level. Conclusions: QTc prolongation may be common in schizophrenia patients who receive clozapine in real world settings; this is a matter of much concern. Potential predictors of QTc prolongation need to be identified and these predictors and their interactions require to be explored in studies with greater statistical power.