Impact of Once-Daily Versus Twice-Daily Dosing Frequency on Adherence to Chronic Medications among Patients with Venous Thromboembolism

BACKGROUND Multiple daily dosing may be negatively associated with patient medication adherence; however, adherence-related data are lacking in a patient population with venous thromboembolism (VTE). OBJECTIVE To assess the adherence rates between once-daily (OD) and twice-daily (BID) dosing regimens of chronic medications in patients with VTE. METHODS We analyzed the PharMetrics Integrated Claims database (claims of commercial insurers in the US) from 1 January 2004, through 31 December 2009. Adult patients with continuous insurance coverage, newly initiated on diabetes mellitus or hypertension medication, and having at least one VTE diagnosis were included. Adherence to OD and BID therapies was calculated by using two measures: medication possession ratio (MPR) and proportion of days covered (PDC). Adherence was defined as an MPR or PDC ≥0.8. Multivariate logistic regressions were conducted to compare the probability of adherence between the OD and BID groups adjusting for baseline confounders. RESULTS A total of 4,867 OD and 1,069 BID patients were identified. Mean duration of exposure to therapy for OD and BID patients was 386 and 356 days (p = 0.011), respectively. Based on MPR, 69 % of OD and 62 % of BID patients were adherent (p < 0.001). For PDC at 12 months, the proportion of adherent patients for the OD and BID groups was 45 and 36 % (p < 0.001), respectively. Adjusted odds ratios (95 % CI) of adherence for the OD relative to BID group were 1.61 (1.37-1.89) based on MPR (p < 0.001) and 1.46 (1.16-1.83) based on PDC at 12 months (p = 0.001). CONCLUSIONS This study demonstrates that VTE patients treated with chronic medications on OD dosing regimens were associated with an approximately 39-61 % higher likelihood of adherence compared with subjects on BID dosing regimens.