Predictors of non-adherence to aromatase inhibitors among commercially insured women with breast cancer

The purpose of this study is to investigate 1-year adherence rates to aromatase inhibitors (AI) and to determine risk factors for non-adherence among commercially insured post-menopausal breast cancer patients. A retrospective cohort of 13,593 commercially insured breast cancer patients with a prescription claim for an AI therapy (exemestane, anastrozole, and letrozole) in 2006 were identified using the MarketScan® Commercial Claims and Encounters Database. Adherence was calculated by the medication possession ratio (MPR) for a 1-year period following the initial claim in 2006. The main outcome variable was non-adherence (<80% MPR) to AI therapy. Multivariate logistic regression was used to determine predictors of non-adherence. Over a 1-year period, 23% of patients were non-adherent with their AI therapy. AI non-adherence was associated with younger age, out-of-pocket costs ≥$30 per AI prescription, as well as with measures during the 12-month period prior to the initial 2006 AI claim of lower patient out-of-pocket total pharmacy costs, no mastectomy, and higher Charlson Comorbidity Index. Non-adherence to AI is a common occurrence. A number of factors were identified that influence patience non-adherence. These factors can be used to identifying patients at increased risk for non-adherence to better target and intervene to support medication taking behaviors.