Initiation of generic imatinib may improve medication adherence for patients with chronic myeloid leukemia

To compare adherence to tyrosine kinase inhibitors (TKIs) between patients with chronic myeloid leukemia (CML) who initiated branded or generic imatinib.

We used MarketScan commercial claims data (January 2011-June 2018) to identify patients with CML who newly initiated branded imatinib before 1 August 2015 or generic imatinib on or after 2 February 2016, and were continuously enrolled in health plans for 6 months before through 6 months following their initial fill. After inverse probability of treatment weighting, we compared adherence (proportion of days covered [PDC]) and persistence (no gaps ≥30 and ≥60 consecutive days in therapy) to TKI therapy.

Patients initiating generic imatinib consistently had higher average PDC per month and over the 6-month follow-up period than initiators of branded imatinib. Average 6-month PDC was 92% (95%CI:89%-94%) for generic initiators and 85% (95%CI:83%-86%) for brand initiators. Compared with branded imatinib initiators, a larger proportion of generic imatinib initiators were adherent and persistent to TKI therapy (PDC ≥ 90%:78% versus 64%; no≥60-day gap:94% versus 86%).

Patients initiating generic imatinib achieved clinically significant improvements in adherence to TKI therapy relative to branded drug users, presumably due to lower out-of-pocket costs. Given the importance of optimal adherence in CML, considering barriers to adherence (eg, patient-cost sharing and health benefit design) when selecting initial treatment may improve long-term medication adherence. Pharmacoepidemiologic studies should consider how best to account for expected cost-sharing and its impact on adherence and subsequent clinical outcomes.