Switching, Persistence and Adherence to Statin Therapy: a Retrospective Cohort Study Using the Australian National Pharmacy Data

Background Statins are widely prescribed for the primary and secondary prevention of cardiovascular disease (CVD), but their effectiveness is dependent on the level of adherence and persistence. Objectives This study aimed to explore the patterns of switching, adherence and persistence among the Australian general population with newly dispensed statins. Methods A retrospective cohort study was conducted using a random sample of data from the Australian national prescription claims data. Switching, adherence to and persistence with statins were assessed for people starting statins from 1 January 2015 to 31 December 2019. Switching was defined as either switching to another intensity of statin, to another statin or to a non-statin agent. Non-persistence to treatment was defined as discontinuation (i.e. ≥90 days with no statin) of coverage. Adherence was measured using proportion of days covered (PDC), and patients with PDC < 0.80 were considered non-adherent. Cox proportional hazard models were used to compare discontinuation, switching and reinitiation between different statins. Results A cohort of 141,062 people dispensed statins and followed over a median duration of 2.5 years were included. Of the cohort, 29.3% switched statin intensity, 28.4% switched statin type, 3.7% switched to ezetimibe and in 2.7%, ezetimibe was added as combination therapy during the study period. Overall, 58.8% discontinued statins based on the 90-day gap criteria, of whom 55.2% restarted. The proportion of people non-adherent was 24.0% at 6 months to 49.0% at 5 years. People on low and moderate intensity statins were more likely to discontinue compared to those on high-intensity statins (hazard ratio [HR] 1.20, 95% confidence interval [CI] 1.09–1.31), (HR 1.28, 95%CI 1.14–1.42), respectively. Compared to maintaining same statin type and intensity, switching statins, which includes up-titration (HR 0.77, 95%CI 0.70 to 0.86) was associated with less likelihood of discontinuation after reinitiation. Conclusions Long-term persistence and adherence to statins remains generally poor among Australians, which limits the effectiveness of these medicines and the consequent health impact they may provide for individuals (and by extension, the population impact when poor persistence and adherence is considered in the statin-taking population). Switching between statins is prevalent in one third of statin users, although any clinical benefit of the observed switching trend is unknown. This, combined with the high volume of statin prescriptions, highlights the need for better strategies to address poor persistence and adherence.