NO DIFFERENCE IN INFUSION REACTIONS BETWEEN ORIGINATOR AND BIOSIMILAR RITUXIMAB

K GOH 1, D LIM 2, M JOVANOVIC 2, D HINE 3, H GOCK 1,2,4

1Department of Nephrology, St Vincent’s Hospital Melbourne, Melbourne, Australia, 2Department of Pharmacy, St Vincent’s Hospital Melbourne, Melbourne, Australia, 3Ambulatory Treatment Centre, St Vincent’s Hospital Melbourne, Melbourne, Australia, 4Department of Medicine, St Vincent’s Hospital, University of Melbourne, Melbourne, Australia

Aim: Identify outpatients switched from MabThera® to Riximyo®, their prescribing units, on-or-off-label indications, differences in infusion-related reactions and efficacy.

Background: Rituximab is an anti-CD20 monoclonal antibody used to treat many B-cell-related disorders.  MabThera® ($1199.22/500mg) is now off-patent and the biosimilar Riximyo® ($299.83/500mg) has become the default preparation at our institution. Concerns that switching MabThera® to Riximyo® increased infusion reactions prompted an audit of the outpatient infusions.

Methods: Pharmacy records identified consecutive patients dispensed Riximyo® between 10/10/2019-04/01/2021 that were previously given MabThera®. Hospital records were used to determine prescribing units, indications and infusion reactions. Follow-up correspondence was used to gauge efficacy.  Infusion reactions were graded nil, mild (symptomatic management, infusion completed), moderate (alteration of vital signs, infusion completed), and severe (infusion discontinued and/or hospital admission).

Results: Outpatients identified (n=43) were from rheumatology (44%), haematology (40%), nephrology (9%) and neurology (7%) units. Off-label-use rate of 23% was predominantly from nephrology and haematology. There was one severe infusion reaction with MabThera® and 2 moderate reactions from Riximyo® (the latter both in the same patient).  2 patients had mild reactions to MabThera® but not Riximyo®, 5 patients vice versa, and one patient with both. There was no difference in reaction rates between the preparations (p=0.29). The majority of patients with information available had positive responses to both preparations (MabThera® 35/37, Riximyo® 25/35). 40% of those with no or yet-unclear response to Riximyo® were haematology patients with progressive lymphoma.

Conclusion: Switching from MabThera® to Riximyo® is not associated with significant increase in infusion reactions. Timing bias is inherent in efficacy assessment given MabThera® was prescribed earlier in disease course, however Riximyo® was still efficacious for most indications of use.


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