Antiarrhythmic drug interactions: are they important?

Most cardiac patients who have cardiac arrhythmias and are treated by antiarrhythmic agents will receive other cardiovascular drugs to treat coexistent problems, for example heart failure, angina or hypertension. Also, two antiarrhythmic drugs may be simultaneously prescribed to these patients in the search for better efficacy and fewer side effects. Finally these patients may well take noncardiovascular drugs such as cimetidine for the treatment of peptic ulcer disease or other hypersecretory disorders. In all cases, complex pharmacodynamic and pharmacokinetic drug interactions are likely to occur. These interactions have been extensively reviewed by Bigger and Giardina. The purpose of this work is to focus on the potentially important interactions with antiarrhythmic drugs. It is of interest for the cardiologist to be aware of the most common and meaningful drug interactions in order to prevent lack of efficacy or a risk of drug toxicity that could result from the simultaneous administration of different drugs to a patient. In this regard the interactions of antiarrhythmic drugs with digitalis, cimetidine, beta-blocking agents and other antiarrhythmic drugs will be briefly reviewed.