Association between refill adherence to lipid-lowering medications and the risk of cardiovascular disease and mortality in Swedish patients with type 2 diabetes mellitus: a nationwide cohort study

OBJECTIVES To analyse the association between refill adherence to lipid-lowering medications, and the risk of cardiovascular disease (CVD) and mortality in patients with type 2 diabetes mellitus. DESIGN Cohort study. SETTING National population-based cohort of Swedish patients with type 2 diabetes mellitus. PARTICIPANTS 86 568 patients aged ≥18 years, registered with type 2 diabetes mellitus in the Swedish National Diabetes Register, who filled at least one prescription for lipid-lowering medication use during 2007-2010, 87% for primary prevention. EXPOSURE AND OUTCOME MEASURES Refill adherence of implementation was assessed using the medication possession ratio (MPR), representing the proportion of days with medications on hand during an 18-month exposure period. MPR was categorised by five levels (≤20%, 21%-40%, 41%-60%, 61%-80% and >80%). Patients without medications on hand for ≥180 days were defined as non-persistent. Risk of CVD (myocardial infarction, ischaemic heart disease, stroke and unstable angina) and mortality by level of MPR and persistence was analysed after the exposure period using Cox proportional hazards regression and Kaplan-Meier, adjusted for demographics, socioeconomic status, concurrent medications and clinical characteristics. RESULTS The hazard ratios for CVD ranged 1.33-2.36 in primary prevention patients and 1.19-1.58 in secondary prevention patients, for those with MPR ≤80% (p<0.0001). The mortality risk was similar regardless of MPR level. The CVD risk was 74% higher in primary prevention patients and 33% higher in secondary prevention patients, for those who were non-persistent (p<0.0001). The mortality risk was 6% higher in primary prevention patients and 18% higher in secondary prevention patients, for non-persistent patients (p<0.0001). CONCLUSIONS Higher refill adherence to lipid-lowering medications was associated with lower risk of CVD in primary and secondary prevention patients with type 2 diabetes mellitus.