Impact of Daily Dosing Frequency on Adherence to Chronic Medications Among Nonvalvular Atrial Fibrillation Patients

Multiple daily dosing may be negatively associated with patient medication adherence, but the findings are inconclusive. The objective of this study was to compare adherence rates to once-daily (q.d.) versus twice-daily (b.i.d.) dosing regimen of chronic medications in patients with nonvalvular atrial fibrillation (AF). The authors analyzed the PharMetrics Integrated Claims database from January 1, 2004 to December 31, 2009. Adult patients with continuous insurance coverage, newly initiated on diabetes or hypertension medication, and having at least one AF diagnosis with no valvular heart disease or valve replacement procedures were included. Compliance to q.d. and b.i.d. therapies was calculated in two ways: medication possession ratio (MPR) and proportion of days covered (PDC). Adherence was defined as an MPR or PDC a parts per thousand yen0.8. Multivariate logistic regressions were conducted to compare the probability of adherence between the q.d. and b.i.d. groups adjusting for baseline confounders. A total of 8,256 q.d. and 2,441 b.i.d. patients were identified. The mean duration of exposure to therapy for q.d. and b.i.d. patients was 447 and 406 days (P < 0.001), respectively. Based on MPR, 75.3% of q.d. and 70.4% of b.i.d. patients were adherent (P < 0.001). For PDC at 12 months, the proportion of adherent patients for the q.d. and b.i.d. groups was 56.5% and 49.6% (P < 0.001), respectively. Adjusted odds ratios (95% CI) of adherence for the q.d. relative to b.i.d. group were 1.26 (1.13, 1.41) based on MPR and 1.23 (1.07, 1.41) based on PDC at 12 months. This study demonstrates that nonvalvular AF patients treated with q.d. dosing regimens for chronic medications were associated with approximately a 26% higher likelihood of adherence compared with subjects on b.i.d. regimens.