Objective: To examine medication adherence among Medicare Part D beneficiaries initiating oral anti-diabetic medications and explore whether there is any association of using mail-order pharmacy (vs. retail pharmacy) with better adherence in this patient population.
Research design and methods: Using administrative pharmacy claims data, we conducted a retrospective cohort study on Medicare Part D beneficiaries who newly initiated oral anti-diabetic treatment between July 1, 2008 and December 31, 2008. Mail-order pharmacy users were matched to retail pharmacy users via propensity scoring, controlling for patient demographic and clinical characteristics. Adherence with oral anti-diabetic medications during the benefit year of 2009 was assessed using the proportion of days covered (PDC). Comparison of medication adherence between the mail-order pharmacy group and retail pharmacy group was conducted in the propensity matched sample using the paired t-tests and McNemar's tests.
Results: A total of 22,546 patients who initiated oral anti-diabetic medications were identified. The average PDC was 0.60 and only 41.6% of the study population attained good adherence (defined as PDC ≥ 0.8) with oral anti-diabetic medications during calendar year 2009. The matched sample included 1361 patients in each of the mail-order and retail pharmacy cohorts. Compared with the retail pharmacy group, mail-order pharmacy users demonstrated a significantly higher PDC (0.68 vs. 0.61; P < 0.001) throughout the benefit year. More patients in the mail-order pharmacy group (49.7%) attained good adherence with their oral anti-diabetic medications compared to 42.8% in the retail pharmacy group (P < 0.001).
Limitations: The study was subject to limitations inherent in retrospective claims database analysis.
Conclusions: Adherence with oral anti-diabetic medications among Medicare Part D beneficiaries is suboptimal. Patients using mail-order pharmacy had better adherence to oral anti-diabetic medications than those who used retail pharmacies. However, the causal relationship between mail-order pharmacy use and adherence should be further examined in a randomized study setting.