Clinical efficacy of generic imatinib

Generic imatinib has recently been approved for chronic myeloid leukemia in Canada and the European Union (EU). There are anecdotal concerns of reduced efficacy related to generic vs. brand name imatinib.

MEDLINE and EMBASE were searched. Generic imatinib product monographs approved by Health Canada and the European Medicines Agency (EMA) were reviewed. Medical information of Novartis, Teva and Apotex were contacted.

Several issues have been raised. First, generic imatinib approved outside Canada and the European Union has been associated with reduced efficacy in small case reports and contradictory findings with two case series. However, the clinical bioequivalence of these generic products has not been clearly established. Secondly, use of generic imatinib in other populations has been questioned. However, imatinib absorption is not significantly different in pediatric chronic myeloid leukemia or patients with gastrointestinal tumours compared to adults with chronic myeloid leukemia. Although reduced absorption was reported after gastric bypass and gastrectomy, imatinib absorption occurs mostly in the ileum, duodenum, colon and jejunum. Change in gastric acidity has also been shown to not affecting imatinib absorption. Finally, beta-crystal form of brand name imatinib is more stable than the alpha-crystal form of generic imatinib at room temperature. However, the EMA found both crystal forms to be highly soluble and polymorphism would not significantly influence the performance of generic imatinib.

Overall, anecdotal concerns appear to be unfounded for generic imatinib approved in Canada and the EU. There is no evidence that these generic imatinib products are less effective than brand name imatinib.