Which one of the following drugs is most likely to block K+ channels in the heart responsible for cardiac repolarization, and also blocks calcium channels in the AV node?
A. Amiodarone
B. Quinidine
C. Lidocaine
D. Sotalol
E. Verapamil
Answer: A. Amiodarone is a highly effective antiarrhythmic drug, in part
because of its multiple actions, which include Na+ channel block, beta
adrenoceptor block, K
- channel block, and Ca2+ channel block. Drugs that
block K - channels prolong APD and ERP and predispose toward torsades de
pointes ventricular arrhythmias. Quinidine, class Ia, can block both sodium
and potassium channels but not calcium channels. Lidocaine, class Ib, blocks
only sodium channels. Sotalol is both a beta blocker and a potassium channel
blocker. It is a class III drug that also has class II properties. Verapamil is a
class IV calcium channel blocker with no effect on potassium.