Does age modify the relationship between adherence to secondary prevention medications and mortality after acute myocardial infarction? A nested case-control study

PURPOSE: Clinical trials have shown that evidence-based secondary prevention medications reduce mortality after acute myocardial infarction (AMI). Yet, these medications are generally underused in daily practice, and older people are often excluded from drug trials. The purpose of this study was to examine whether the relationship between adherence to evidence-based drugs and post-AMI mortality varies with increasing age. METHODS: The study population was defined as all residents in the Local Health Authority of Bologna (Italy) hospitalized for AMI between January 1, 2008 and June 30, 2011, and followed up until December 31, 2012. Medication adherence was calculated as the proportion of days covered (PDC) for filled prescriptions of angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, β-blockers, antiplatelet drugs, and statins; patients were classified as adherent (PDC ≥75 %) or nonadherent (PDC <75 %). We used incidence density sampling, and the moderating effect of age on the relationship between adherence and mortality was investigated through conditional multiple logistic regression analysis. RESULTS: The study population comprised 3963 patients. During the 5-year study period, 1085 deaths (27.4 %) were observed. For both younger and older patients, adherence to polytherapy (three or four medications) was associated with lower mortality (adj. rate ratio = 0.41; P < 0.001). A significant inverse relationship was found between adherence to each of the four medications and mortality, although the risk reduction associated with antiplatelet therapy declined after the age of 70-75. CONCLUSIONS: The beneficial effect of evidence-based polytherapy on mortality following AMI is observed also in older populations. Nevertheless, the risk-benefit ratio associated with antiplatelet therapy is less favorable with increasing age.