P1107 Biosimilar but not quite the same?: Post-induction levels of infliximab differ between brands

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Abstract Background Infliximab is used for the induction and maintenance of clinical remission in Crohn’s disease and ulcerative colitis. Our trust underwent a switch from the infliximab preparation Inflectra to the biosimilar Remsima in 2022. We wished to analyse if levels of treatment persistence and response were similar between brands as anecdotally we observed a potential higher rate of primary treatment failure, loss of response and requirement for dose escalation of Remsima when compared to Inflectra post-induction. Methods Patients were identified from our IBD database. Post-induction levels of infliximab were assessed. Infliximab levels pre- and post-switch from Inflectra to Remsima were assessed. Rates of dose escalation and switch to alternative agents and reasons for switch were also examined. Statistical analysis was completed using Mann-Whitney U test and Fisher’s exact test. Results In total, 82 patients were included in our analysis; 42 with Crohn’s disease and 40 with ulcerative colitis. 35 received induction with Inflectra and subsequently switched to Remsima. 47 patients received Remsima induction. Post-induction levels with Inflectra showed a mean of 8.08 mcg/ml when compared to Remsima levels of 5.01 mcg/ml (p = 0.02642). Pre-switch levels of Inflectra were almost equivocal at 8.44 mcg/ml when compared to maintenance levels of 8.57 mcg/ml (p = 0.177) for Remsima. 13 patients (27.7%) who received Remsima induction required dose-escalation compared to 20% of those induced with Inflectra (p = 0.4508). 40% of patients on Inflectra switched to another class of biologic were switched due to loss of response/failure to respond or inadequate drug levels with high antibodies compared to 47% of those switched from Remsima (p = 0.621) for the same reasons. Conclusion Post-induction trough levels of infliximab differ between brands. This should be taken into consideration when considering higher dosing at induction or for those patients treated with infliximab for acute severe colitis and earlier accelerated dosing should be considered in those patients treated with Remsima who have a slow clinical response to treatment. Trough levels once established on the drug appear to be similar and rates of switching out of class due to failure to respond/loss of response and antibody formation comparable.