Objective: The American College of Cardiology (ACC) and the American Heart Association (AHA) recommend adherence monitoring within 4 to 12 weeks following statin initiation. The objective of the study was to understand adherence of statins and their key predictors which could be used in adherence monitoring.

Methods: A systematic literature review using PRISMA guidelines was conducted in June 2020. Key search terms (cardiovascular disease, atherosclerosis, adherence, statins) were used in multiple combinations in PubMED and MEDLINE to identify studies. Studies conducted among humans, during the period 2012-20, within the US and using retrospective observational methods were included. Studies without adherence as the primary outcome, economic models, randomized control trials and reviews were excluded. Screening, data extraction and qualitative analysis were conducted by two independent researchers.

Results: 241 initial studies were identified, title and abstracts of 80 studies were reviewed and 28 studies were included in the final review. Twenty studies reported proportion of days covered (PDC) as a dichotomous outcome; the percentage of patients with PDC ≥80% ranged from 29.2% to 74.2%. Eleven studies reported a continuous outcome of PDC, with mean values ranging from 0.57 to 0.86. Four studies reported medication possession ratio (MPR) as a dichotomous outcome; the percentage of patients with MPR > 80% ranged from 45.3% to 75%. Common positive predictors of adherence were care coordination issues with healthcare providers (N=7), followed by medication-related issues (N=4), and presence of chronic disease (N=3). Negative predictors of adherence were high co-morbidity burden (N=3), and prescription of high intensity statin (N=2).

Conclusion: A majority of studies reported higher adherence levels in more than 50% of patients. Care-coordination issues with health care providers was most commonly identified as an important predictor of medication adherence among patients.