Patients with chronic-phase chronic myeloid leukemia (CP-CML) are more likely to switch from generic imatinib than brand-name imatinib, largely due to adverse events, according to a study of Canadian patients with CML. The study was recently published in Haematologica.1

“If physicians are putting their patients on generic, they shouldn’t think it’s exactly the same as brand-name,” said lead author Adi Klil-Drori, MD, clinical fellow at the Sunnybrook Health Sciences Centre and the University of Toronto, Ontario, in an interview with Cancer Therapy Advisor. “Especially in Canada, where privately insured patients have the opportunity to switch, they may not feel comfortable with a new treatment option. Physicians should keep that in mind, especially over the first few months.”

To form the source population of their matched cohort study, Dr. Klil-Drori and his coauthors identified the records of patients with CP-CML in the province of Québec, Canada, who used generic imatinib (GI) for the first time from 2013 onward. This was feasible because 2 versions of GI were approved in Canada in April 2013 and reimbursed for patients with public drug insurance starting in October 2013. Gradually, patients with public or private insurance were required to switch from brand-name imatinib (BI) to GI unless they had a “do not substitute” order. “This transition period,” the coauthors wrote, “allowed for the examination of contemporaneous use of BI and GI.”

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The matched cohorts (either GI or BI) included 167 patients each. To ensure compatibility, BI users were matched with GI users based on use at the same calendar date, nearest duration of prior BI use, and closest age. The researchers’ goal was to assess nonpersistence, which they defined as a “switch to an alternate tyrosine kinase inhibitor (TKI) within 45 days of stopping the TKI used at cohort entry.” In doing so, they’d determine the tolerability of GI compared to BI, along with recording what ultimately caused the switch.

At 3 years follow-up, persistence with GI use was 72.8% (95% confidence interval [CI], 63.9%–81.6%) as compared with 88.2% for BI use (95% CI, 82.8%–93.6%, P =.03). In the first 6 months, 23 patients switched from GI and 16 patients switched from BI, making up 63.9% and 94.1% of switchers overall, respectively. Overall, the probability of switching among GI users was twice as high as among BI users (hazard ratio [HR], 2.13; 95% CI, 1.18–3.86).

Adverse events were cited as the main reason for stopping GI; most were grade 2 or lower, though there were 10 nonhematologic grade 3 adverse events in 7 patients. Twenty-five of the 36 switchers (69.5%) from GI noted intolerance, while 12 (33.3%) noted resistance.

Previous studies have indicated that toxicity is a key reason why patients take — or don’t take — TKIs, regardless of if the TKI is on-brand or is available as a generic medication.2,3