Severe Hypersensitivity Reactions at Biosimilar versus Originator Rituximab Treatment Initiation, Switch and Over Time: A Cohort Study on the French National Health Data System.

Background: Biosimilar products of rituximab came to market in 2017. French pharmacovigilance centers have highlighted an excess of case reports of severe hypersensitivity reactions related to their use compared with the originator product.

Objective: The aim of this study was to assess the real-world association between biosimilar versus originator rituximab injections and hypersensitivity reactions, among initiators and switchers, at first injection and over time.

Methods: The French National Health Data System was used to identify all rituximab users between 2017 and 2021. A first cohort consisted of patients who initiated rituximab (originator or biosimilar), while a second cohort consisted of originator-to-biosimilar switchers, matched on age, sex, deliveries history, and pathology, with one or two patients still receiving the originator product. The event of interest was defined as a hospitalization for anaphylactic shock or serum sickness following a rituximab injection.

Results: A total of 91,894 patients were included in the initiation cohort-17,605 (19%) with the originator product and 74,289 (81%) with a biosimilar. At initiation, 86/17,605 (0.49%) and 339/74,289 (0.46%) events occurred in the originator and biosimilar groups, respectively. The adjusted odds ratio of biosimilar exposure associated with the event was 1.04 (95% confidence interval [CI] 0.80-1.34), and the adjusted hazard ratio for biosimilar versus originator exposure was 1.15 (95% CI 0.93-1.42), showing no increased risk of event with biosimilar use at first injection, and over time. 17,123 switchers were matched to 24,659 non-switchers. No association was found between switch to biosimilars and occurrence of the event.

Conclusion: Our study does not support any association between exposure to rituximab biosimilars versus originator and hospitalization for a hypersensitivity reaction, either at initiation, at switch, or over time.