Patients on antipsychotic treatment have higher risk of cardiac events

Haloperidol and thioridazine are the most widely used typical antipsychotic drugs in the United States. Cross sectional data suggest that thioridazine may prolong the QT interval more than haloperidol, although only one experimental study has compared the QT effects of these drugs in humans. In that study, haloperidol 15°mg/day prolonged the Bazett-corrected interval (QTcB) an average of 4.7°ms (95% confidence interval -2.0 to 11.3) whereas thioridazine 300°mg/day prolonged the QTcB by 35.6°ms (30.5°to 40.7). The importance of this degree of prolongation is not known. 1Hennessy et al. compared the frequency of cardiac arrest and ventricular arrhythmia associated with different antipsychotic drugs, in particular comparing thioridazine to haloperidol.A cohort study of outpatients with schizophrenia treated with clozapine, haloperidol, risperidone, or thioridazine were compared to a control group of patients with glaucoma; and a control group of patients with psoriasis.The primary end point was the rate of cardiac arrest or ventricular arrhythmia. They found patients with treated schizophrenia had higher rates of cardiac arrest and ventricular arrhythmia than controls, with rate ratios ranging from 1.7°to 3.2. ° Overall, thioridazine was not associated with an increased risk compared with haloperidol (rate ratio 0.9, °95% confidence interval 0.7°to 1.2). However, thioridazine showed an increased risk of events at doses ≥600 mg (2.6, °1.0°to 6.6; P=0.049) and a linear dose-response relation (P=0.038).1The authors write, 'The increased risk of cardiac arrest and ventricular arrhythmia in patients with treated schizophrenia could be due to the disease or its treatment. Overall, the risk with thioridazine was no worse than that with haloperidol. Thioridazine may, however, have a higher risk at high doses, although this finding could be due to chance. To reduce cardiac risk, thioridazine should be prescribed at the lowest dose needed to obtain an optimal therapeutic effect.' 1Reference...