Purpose: To compare adherence to tyrosine kinase inhibitors (TKIs) between patients with chronic myeloid leukemia (CML) who initiated branded or generic imatinib.
Methods: 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.
Results: 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%).
Conclusions: 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.
Keywords: adherence; cancer; imatinib; persistence; pharmacoepidemiology.
© 2019 John Wiley & Sons, Ltd.