Adherence to evidence-based therapies after acute coronary syndrome: a retrospective population-based cohort study linking hospital, outpatient, and pharmacy health information systems in Valencia, Spain.

BACKGROUND: Pharmacological secondary prevention in patients after an acute coronary syndrome (ACS) has contributed substantially to reductions in cardiovascular morbidity and mortality and, overall, has undergone important improvements in recent years. Nevertheless, there is still a considerable adherence gap and opportunity for improvement.
OBJECTIVE: To assess, in a cohort of patients who survived an ACS, adherence to commonly prescribed secondary prevention drugs, factors associated to adherence, and variations among health care delivery areas.
METHODS: We combined the medical and pharmacy databases from a regional public health service in Valencia, Spain, to construct a population-based cohort of patients discharged alive after an emergency admission for an ACS to any hospital of the Valencia Health Agency in 2008. We evaluated medication adherence by determining the proportion of days covered (PDC) for each therapeutic group (antiplatelet agents, beta-blockers, angiotensin antagonists, and statins) in the 9 months following hospital discharge. Fully adherent patients were defined as those having enough treatment to cover 75% (PDC75) of the follow-up period.
RESULTS: The study cohort consisted of 7,462 patients. PDC75 was reached by 69.9% of patients taking antiplatelet agents, 43.3% taking beta-blockers, 45.4% taking angiotensin antagonists, and 58.8% taking statins. Approximately 18% of patients did not reach PDC75 with any treatment, while 47.6% did so for 3 or more therapeutic groups. Lower adherence was found in diagnoses other than myocardial infarction. Other factors associated with nonadherence were older age, women, having copayment, foreign born, and most comorbidities (except for hypertension and hyperlipidemia, which were inversely associated, and diabetes and peripheral disease, which were not significantly associated). Health care delivery areas showed certain variability in their performance on these adherence measures that remained after the adjustment for covariates, although confidence intervals overlapped except between areas at the extremes.
CONCLUSIONS: The proportion of fully adherent patients remains suboptimal, and important improvements are still possible in secondary prevention of ischemic heart disease. The combination of electronic health information systems may be very useful for monitoring adherence and evaluating the effectiveness of adherence and other quality improvement interventions.