Comparative cardiac safety of low‐dose thioridazine and low‐dose haloperidol

Aim To compare the rate of ventricular arrhythmia, sudden death and unexplained or unattended death among users of thioridazine and haloperidol. Methods Observational cohort study of thioridazine and haloperidol users in the UK General Practice Research Database (GPRD) using data from 1987 through 29 June 2000. Patients were followed for 30 days following each study prescription. The event of interest was a diagnosis of ventricular arrhythmia, sudden death, or unexplained or unattended death. Cox regression was used to calculate rate ratios (RRs) and 95% confidence intervals (CIs), to examine potential confounding factors, and to examine dose–response relationships. Results Use of thioridazine and haloperidol in the GPRD was primarily in older patients, at low dose (median daily dose 31 mg thioridazine, 1.8 mg haloperidol). There was no association between thioridazine use and the rate of ventricular arrhythmia, sudden death, and unexplained or unattended death (adjusted RR 0.9, 95% CI 0.7, 1.1). The rate did not appear to increase with dose for either drug over the range observed. Conclusions These results suggest that low‐dose thioridazine and haloperidol have similar cardiac safety.