Introduction: Non-adherence to cardioprotective medications is associated with mortality after myocardial infarction (MI) in patients with diabetes. Therefore, identifying predictors of medication adherence could inform optimal secondary prevention after MI. We examined whether glycemic control among those with diabetes was associated with post-MI cardioprotective medication adherence.
Methods: We studied 7,269 US Veterans with type 2 diabetes who were hospitalized for a primary diagnosis of first MI from 2011-2014, survived for one year, and prescribed a statin, beta-blocker, and angiotensin converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB). The primary exposure was poor glycemic control at the time of MI, defined as hemoglobin A1c (HbA1c) ≥9%. A secondary exposure was HbA1c, categorized as <6%, 6-6.9%, 7-7.9%, 8-8.9%, and ≥9%. The primary outcome was one-year adherence to each medication class (statin, beta-blocker, and ACEi/ARB) and to all three medication classes, defined as proportion of days covered exceeding 0.8. We used adjusted risk differences and multivariable Poisson regression to compare rates of medication adherence between individuals, adjusting for demographic and clinical covariates.
Results: Seventy-nine percent (n=5747) of participants had HbA1c <9%, and 21% (n=1522) had HbA1c ≥9%. Compared to those with HbA1c <9%, those with HbA1c ≥9% had lower rates of adherence (65% vs 73% for statin, 70% vs 79% for beta-blocker, 73% vs 80% for ACEi/ARB, and 49% vs 58% for all three, all p<0.0001; adjusted risk difference of 8.9% [95% CI 6.0, 11.8] for adherence to all three medications). Relative to those with HbA1c 6-6.9%, there was a non-significant trend towards lower medication adherence among those with HbA1c <6%, and adherence to all three medications declined with increasing HbA1c (risk ratio [RR] 0.99 [0.94, 1.04], 0.93 [0.87, 0.99], 0.82 [0.77, 0.88] for those with HbA1c 7-7.9%, 8-8.9%, and ≥9%, respectively; Figure).
Conclusion: While medication adherence overall declined with worsening glycemic control, the greatest differences are seen in those with a HbA1c ≥9%. Thus, targeting optimal medical therapy adherence, in addition to glycemic control, could benefit those with poorly-controlled diabetes after MI.