Real-World Evidence Assessing the Safety of Administering Intravenous Rituximab Biosimilar in the First Cycle and Subcutaneous Rituximab in Subsequent Cycles in B-Cell Lymphoma Patients

<b>Background:</b> Biosimilar versions of rituximab have similar safety and efficacy as the reference product across all indications based on the extrapolation principle. Our organization replaced intravenous (IV) rituximab (Mabthera) with IV rituximab (Truxima-Biosimilar) in 2021. Hence, our practice changed to providing first cycles of IV rituximab (Truxima-Biosimilar) instead of rituximab (Mabthera), and if the first cycle was completed without severe infusion-related reactions (IRRs), then subsequent cycles were given with subcutaneous (SC) rituximab as per institutional guidelines. However, the safety of this approach has not been evaluated. <b>Methods:</b> A retrospective study was conducted at the Princess Nourah Oncology Center in Saudi Arabia. The primary objective was to assess IRRs after using IV rituximab (Truxima-Biosimilar) in the first cycle followed by SC rituximab in subsequent cycles. <b>Results:</b> Of the 71 patients reviewed, 35 patients met the eligibility criteria. Only one (3%) patient developed an IRR. However, it was a Grade 1 IRR, as per CTCAE.V5, and the patient was able to complete the remaining IV infusion successfully. Hence, all patients transitioned from IV rituximab biosimilar to SC rituximab Mabthera. <b>Conclusions:</b> This real-world study demonstrates that transitioning from IV rituximab biosimilar to SC Mabthera is a well-tolerated and safe practice, confirming the extrapolation principle of biosimilars.