β-Blocker Dosages and Mortality After Myocardial Infarction

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Abstract
DESPITE the fact that numerous large, randomized, placebo-controlled trials have demonstrated a beneficial effect of long-term β-blocker therapy in patients after an acute myocardial infarction,1 these drugs are greatly underused by practicing clinicians.2-5 This underuse appears to be more of a problem in the elderly.6 Moreover, the dosages of β-blockers used in these large, randomized, controlled trials (160 mg of propranolol hydrochloride,7,8 200 mg of metoprolol tartrate per day,9 and 100 mg of atenolol per day10) appear to be much larger than those routinely prescribed.2 In fact, Viskin et al2 found that 89% of patients who were discharged from the hospital and prescribed a β-blocker regimen received dosages 50% or less of the dosages shown to be effective in randomized clinical trials. The effectiveness of these lower dosages in reducing morbidity and mortality is unknown. Furthermore, since it is unlikely that any randomized controlled trials will be designed to examine this question, we analyzed data from a large study of patients with acute myocardial infarction to determine the dosages of β-blockers commonly prescribed to infarct survivors and whether these clinically prescribed dosages of β-blockers are associated with the same reduction in cardiovascular mortality as the larger dosages used in randomized controlled trials.