Adherence to evidence-based drug therapies after myocardial infarction: is geographic variation related to hospital of discharge or primary care providers? A cross-classified multilevel design

OBJECTIVES: To measure the adherence to polytherapy after myocardial infarction (MI), to compare the proportions of variation attributable to hospitals of discharge and to primary care providers, and to identify determinants of adherence to medications. SETTING: This is a population-based study. Data were obtained from the Information Systems of the Lazio Region, Italy (5 million inhabitants). PARTICIPANTS: Patients hospitalised with incident MI in 2007–2010. OUTCOME MEASURE: The outcome was chronic polytherapy after MI. Adherence was defined as a medication possession ratio ≥0.75 for at least three of the following drugs: antiplatelets, β-blockers, ACEI angiotensin receptor blockers, statins. DESIGN AND ANALYSIS: A 2-year cohort study was performed. Cross-classified multilevel models were applied to analyse geographic variation and compare proportions of variability attributable to hospitals of discharge and primary care providers. The variance components were expressed as median ORs MORs. If the MOR is 1.00, there is no variation between clusters. If there is considerable between-cluster variation, the MOR will be large. RESULTS: A total of 9606 patients were enrolled. About 63% were adherent to chronic polytherapy. Adherence was higher for patients discharged from cardiology wards (OR=1.56 vs other wards, p<0.001) and for patients with general practitioners working in group practice (OR=1.14 vs single-handed, p=0.042). A relevant variation in adherence was detected between local health districts (MOR=1.24, p<0.001). When introducing the hospital of discharge as a cross-classified level, the variation between local health districts decreased (MOR=1.13, p=0.020) and the variability attributable to hospitals of discharge was significantly higher (MOR=1.37, p<0.001). CONCLUSIONS: Secondary prevention pharmacotherapy after MI is not consistent with clinical guidelines. The relevant geographic variation raises equity issues in access to optimal care. Adherence was influenced more by the hospital that discharged the patient than by the primary care providers. Cross-classified models proved to be a useful tool for defining priority areas for more targeted interventions.