Does a cardiovascular event change adherence to statin treatment in patients with type 2 diabetes? A matched cohort design

Objective: To be effective, adherence to statin treatment is essential. We assessed the effect of an apparent first cardiovascular event on statin adherence rates in type 2 diabetes patients. Research design and methods: A matched cohort study was conducted among type 2 diabetes patients initiating statin treatment for primary prevention in the Groningen University IADB. nl pharmacy database. Patients who had a drug-treated cardiovascular event (index date) after statin initiation were matched to a reference patient without such an event with similar gender, age at statin initiation, initiation date, follow-up period and adherence level before the event. Adherence rates were measured as percentages of days covered (PDC), and shifts in adherence levels (non-adherent/partially adherent/fully adherent) and rates around the event were evaluated. Results: We could match 375 of the 855 eligible index patients to a reference patient. Index patients had on average a PDC of 81% after the index date; reference patients had a PDC of 71% (p<0.001) while both had a PDC of 79% before the index date. Index patients were 4.5 times more likely than reference patients to shift from non-adherent to fully adherent (95% CI 1.1-18.8) and 1.8 times more likely to shift from partially adherent to fully adherent (95% CI 1.2-2.6). In the index group, 26% of patients became more adherent after the first cardiovascular event. In contrast, 20% of patients became less adherent. Limitations: Medication proxies were used, which could have caused misclassification. Furthermore, a substantial group of index patients could not be matched to a reference patient due to small ranges in matching criteria. Conclusions: The occurrence of a drug-treated cardiovascular event appeared to avert the declining statin adherence rate observed in diabetes patients without such an event. On the other hand, one in five patients became less adherent after the event, indicating that there are still important benefits to achieve.