Healthcare resource utilization and costs associated with non-adherence to imatinib treatment in chronic myeloid leukemia patients

Background: Patients with chronic myeloid leukemia (CML) who do not adhere to treatment may experience suboptimal outcomes. Objective: To examine the association between adherence with imatinib and direct healthcare costs and resource utilization in a large group of privately insured CML patients. Patients and methods: CML patients under age 65 were identified with ICD-9 code 205.1X using MarketScan Commercial Claims data between 1/1/02 and 7/31/08. Patients were required to be continuously enrolled in a private insurance plan during the baseline and study periods, defined respectively as the 4 months prior to and the 12 months following imatinib initiation. Non-adherence was evaluated by the medication possession ratio (MPR), defined as the fraction of days during the study period that patients had filled prescriptions for imatinib, and stratified into two groups (low MPR: < 85%, high MPR: >= 85%). Costs, inpatient admissions, and hospital days were compared between high and low adherence groups using Wilcoxon tests. Regression models compared utilization and costs controlling for age, sex, CML severity, Charlson comorbidity index, baseline costs, and other factors. Results: The study sample consisted of 592 patients, where 242 (40.9%) patients were classified with a low MPR, while 350 (59.1%) had a high MPR. Mean MPR was 79% (95% confidence interval 76-81%). Patients with a low MPR incurred more all-cause inpatient visits (4.1 vs. 0.4; p < 0.001) and all-cause inpatient days (14.8 vs. 1.8; p < 0.001). Regression models demonstrated a 283% increase (US$56 324; p < 0.001) in non-imatinib costs within the low- vs. high-MPR group. The generalizability of this study is limited by the use of a privately insured population under 65 years of age as well as by the limitations common to claims data analyses. Conclusions: Imatinib adherence is an important issue for patients and physicians. Better imatinib adherence was associated with significantly lower resource utilization and costs in CML patients, as lower imatinib costs in low MPR patients were more than offset by higher non-imatinib costs mostly driven by inpatient services.