Anti-arrhythmic drugs can be classified clinically into those that act on supraventricular arrhythmias (e.g. verapamil hydrochloride), those that act on both supraventricular and ventricular arrhythmias (e.g. amiodarone hydrochloride) and those that act on ventricular arrhythmias (e.g. lidocaine hydrochloride).
Anti-arrhythmic drugs can also be classified according to their effects on the electrical behaviour of myocardial cells during activity, although this classification is of less clinical significance:
- Class I: membrane stabilising drugs (e.g. lidocaine, flecainide)
- Class II: beta-blockers
- Class III: amiodarone; sotalol (also Class II)
- Class IV: calcium-channel blockers (included verapamil but not dihyropyridines)
The negative inotropic effects of anti-arrhythmic drugs tend to be additive. Therefore special care should be taken if two or more are used, especially if myocardial function is impaired. Most drugs that are effective in countering arrhythmias can also provoke them in some circumstances; moreover, hypokalaemia enhances the pro-arrhythmic effect of many drugs.