Indication-Specific Generic Uptake of Imatinib Demonstrates the Impact of Skinny Labeling

Generic competition can be delayed if brand-name manufacturers obtain additional patents on supplemental uses. The US Food and Drug Administration allows generic drug manufacturers to market versions with skinny labels that exclude patent-protected indications. This study assessed whether use of generic versions of imatinib varied between indications included and excluded from the skinny labels.

In this cross-sectional study, we identified adult patients covered by commercial insurance or Medicare Advantage plans who initiated imatinib from February 2016 (first generic availability) to September 2020. Generic versions were introduced with skinny labels that included indications covering treatment of chronic myelogenous leukemia (CML) but excluded treatment of gastrointestinal stromal tumors (GISTs) because of remaining patent protections. Logistic regression was used to determine whether use of generic versus brand-name imatinib differed between patients with a diagnosis of CML or GIST, adjusting for demographics, insurance type, prior use of brand-name drugs, and calendar month.

Among 2,000 initiators, 934 (47%) had CML and 686 (34%) had GIST. Within 3 years after generics entered the market, more than 90% of initiators in both groups used generic imatinib. Initiation of generic imatinib was slightly lower among patients with GIST than among patients with CML (85% v 88%; adjusted odds ratio 0.56; 95% CI, 0.39 to 0.80; P ≤ .001).

Generic versions of imatinib were dispensed frequently for indications both included (CML) and excluded (GIST) from the skinny labeling, although patients with GIST were slightly less likely to receive a generic version. The skinny labeling pathway allowed generics to enter the market before patent protection for treating patients with GIST expired, facilitating lower drug prices.