 Drugs that prolong the QT interval including antiarrhythmics such as quinidine, the antihistamines astemizole and terfenadine, and some antipsychotics may increase the chance of ventricular dysrhythmias.TCAs may enhance the response to alcohol and the effects of barbiturates and other CNS depressants.Side effects may also be enhanced by other drugs that have antimuscarinic properties.