Pharmacological Effects of Antiarrhythmic Drugs

Most antiarrhythmic drugs are potent compounds with a relatively narrow therapeutic index. When prescribed judiciously, they can have a key role in enhancing or prolonging the lives of patients with most common arrhythmias. But when misprescribed, through selection of an inappropriate drug or dosage regimen, the end result may range from inadequate control of the arrhythmia to a proarrhythmic effect. Ultimately, the optimal use of antiarrhythmic drug therapy depends in large part on understanding the pharmacodynamics and pharmacokinetics of each antiarrhythmic drug. Despite the common classification of antiarrhythmic drugs into class I, II, III, or IV, each drug has a unique pharmacological profile and must not be considered interchangeable with other members of its class. Likewise, each patient is unique with respect to the innumerable factors that can alter the pharmacokinetics of an antiarrhythmic drug, including coexisting diseases, concurrent drug therapies, and endogenous or age-related metabolic variations. This article provides an overview of the key pharmacodynamic and pharmacokinetic characteristics of the major antiarrhythmic drugs in use. It also offers specific examples that may be used to ensure that patients receive the most appropriate therapy.