Who benefits from fixed-dose combinations? Two-year statin adherence trajectories in initiators of combined amlodipine/atorvastatin therapy

Purpose: We compared statin adherence in individuals initiating combined amlodipine/atorvastatin therapy as a fixed-dose (FDC) or free combination and identified subgroups benefiting most from FDCs. Methods: We used a 10% sample of Australian Pharmaceutical Benefits Scheme dispensing data (2005-2015) to identify individuals initiating amlodipine and atorvastatin as an FDC (n = 3996) or free combination (n = 5434), with or without prior statin dispensing. We measured the proportion of days covered in each 30-day period over 24 months and classified patterns of statin adherence using group-based trajectory models. We identified predictors of adherence trajectories using logistic regression. Results: The median age was 71 years, and 53% were female. We identified 4 patterns of statin adherence: near-perfect adherence (n = 5383), good adherence (n = 1893), declining adherence (n = 1247), and early nonadherence (n = 907). Compared with the free combination, FDC initiators were more likely to have near-perfect adherence if they were previously statin adherent irrespective of amlodipine dose (amlodipine 5 mg: OR = 1.61, 95% CI 1.38-1.87; amlodipine 10 mg: OR = 2.39, 95% CI 1.63-3.51) or they were previously statin nonadherent and initiated on the 5 mg amlodipine dose (OR = 1.87, 95% CI 1.50-2.32). Statin-naïve individuals initiating on the FDC with 10 mg amlodipine were less likely to have near-perfect adherence (OR = 0.60, 95% CI 0.41-0.88) and more likely to have early nonadherence (OR = 1.73, 95% CI 1.17-2.55). Conclusions: The amlodipine/atorvastatin FDC was associated with greater statin adherence among prevalent statin users, and individuals who initiated on lower amlodipine doses. The FDCs did not improve adherence in statin-naïve individuals and in some cases resulted in poorer adherence.