Amiodarone Interaction With β-Blockers

Abstract

Background —Investigations with in vitro and animal models suggest an interaction between amiodarone and β-blockers. The objective of this work was to explore if an interaction with β-blocker treatment plays a role in the decrease of cardiac arrhythmic deaths with amiodarone in patients recovered from an acute myocardial infarction. Methods and Results —A pooled database from 2 similar randomized clinical trials, the European Amiodarone Myocardial Infarction Trial (EMIAT) and the Canadian Amiodarone Myocardial Infarction Trial (CAMIAT), was used. Four groups of post–myocardial infarction patients were defined: β-blockers and amiodarone used, β-blockers used alone, amiodarone used alone, and neither used. All analyses were done on an intention-to-treat basis. Unadjusted and adjusted relative risks for all-cause mortality, cardiac death, arrhythmic cardiac death, nonarrhythmic cardiac death, arrhythmic death, or resuscitated cardiac arrest were lower for patients receiving β-blockers and amiodarone than for those without β-blockers, with or without amiodarone. The interaction was statistically significant for cardiac death and arrhythmic death or resuscitated cardiac arrest ( P =0.05 and 0.03, respectively). Findings were consistent across subgroups. Conclusions —These findings are based on a post hoc analysis. However, they confirm prior results from in vitro and animal experiments suggesting an interaction between β-blockers and amiodarone. In practice, not only is the adjunct of amiodarone to β-blockers not hazardous, but β-blocker therapy should be continued if possible in patients in whom amiodarone is indicated.