Which of the following drugs can cause Torsades'de pointes?

Ans. (A) Quinidine(Ref: Katzung 10th/e p224; KDT 8th/e p574)*Torsades'de pointes is a polymorphic ventricular tachycardia that is usually caused due to blockade of delayed rectifier K+ channels in the heart.*It manifests in the ECG as QTc prolongation.*Drugs having cardiac K+ channel blocking activities can cause this arrhythmia. These include:-Class Ia antiarrhythmics -Quinidine, Procainamide (Na+ and K+ channel blockers)-Class III antiarrhythmics -Bretylium, sotalol, dofetilide, ibutilide and amiodarone (K+ channel blockers)-Other drugs like Terfenadine, Cisapride, Astemizole, Sparfloxacin, Gatifloxacin, Grepafloxacin, Mefloquine, Pentamidine, Thioridazine, Ziprasidone etc.