Adherence to tyrosine kinase inhibitors among Medicare Part D beneficiaries with chronic myeloid leukemia

Background—Tyrosine kinase inhibitors (TKIs) improve survival of chronic myeloid leukemia (CML) patients dramatically; however, non-adherence to TKI therapy may lead to resistance to the therapy. They are very expensive and covered under Part D insurance for Medicare patients. The impact of low-income subsidy status and cost-sharing on adherence was not well studied in the literature among this group. Methods—Surveillance, Epidemiology, and End Results (SEER) registry data linked with Medicare Part D data from years 2007–2012 was used in this study. We identified 836 CML patients with Medicare Part D insurance coverage who were new TKI users. Treatment nonadherence was defined as a binary variable indicating proportion of days covered (PDC) lower than 80% during the 180-day period after TKI therapy initiation. Logistic regression was used to examine the relationship between out of pocket (OOP) cost per 30-day drug supply, Part D plan characteristics and treatment adherence while controlling for other patient characteristics. Results—Overall 244 (29%) of the 836 CML patients were non-adherent to targeted oral therapy during the 180 days after they began taking the TKIs. The multivariable logistic regression showed that patients with heavily subsidized (OR=6.7, 95% CI: 2.8~15.9) and moderately subsidized (OR=3.0, 95% CI: 1.4~6.5) Part D plans were much more likely to have non-adherence than patients without subsidy. Conclusions—This population-based study found a significantly higher rate of non-adherence among heavily subsidized patients with substantially lower OOP costs, which suggests that future research is needed to help lower the non-adherence rate among these patient