Adherence and dosing frequency of common medications for cardiovascular patients.

Objectives: To compare adherence between once-daily (QD) and twice-daily (BID) dosing with chronic-use prescription medications used by patients with cardiovascular disease.
Study Design: Retrospective cohort database analysis.
Methods: Analysis consisted of 1,077,474 patients aged >18 years with a prescription index date from January 1 to December 31, 2007, for an antidiabetic, antihyperlipidemic, antiplatelet, or cardiac agent with QD or BID dosing. Adherence (medication possession ratio [MPR]) was the number of days of medication supplied between the first prescription fill date and the subsequent 365 days divided by 365 days. Overall mean MPR and comparisons between dosing frequency groups were assessed with a generalized estimating equation. Covariates included age at index date, gender, Charlson comorbidity index, therapeutic class, dosing frequency, and the interaction between therapeutic class and dosing frequency group.
Results: Overall, the adjusted mean MPR ± standard error (SE) value for QD agents was 13.6% greater than BID agents (0.66 ± 0.0006 vs 0.57 ± 0.0016; P <.01). The adjusted mean MPR value for QD agents was 2.9%, 17.5%, and 29.4% greater than BID agents in the antidiabetic, antihyperlipidemic, and antiplatelet therapeutic classes, respectively. For cardiac agents, the adjusted mean MPR value was similar between QD and BID agents. Carvedilol represented approximately 80% of the cardiac agents in the BID group. The adjusted mean MPR ± SE for carvedilol phosphate QD was 0.73 ± 0.0024 and 0.65 ± 0.0027 for carvedilol BID (11% difference; P <.01).
Conclusions: In this large analysis, the QD dosing regimen was related to greater adherence versus a BID regimen.