Relapse of retinal vasculitis after a non-medical biosimilar switch: a case report.

PURPOSE: To describe a case of recurrent ocular inflammation following a non-medical switch between two infliximab biosimilars, highlighting potential clinical implications of biosimilar-to-biosimilar transitions in uveitis management.

CASE DESCRIPTION: A 56-year-old man with intermediate uveitis and retinal vasculitis achieved complete remission on adalimumab but developed anti-drug antibodies after 22 months, prompting transition to infliximab-dyyb (Inflectra) with oral methotrexate. The patient achieved quiescence for two years on this regimen. Due to an insurance formulary change, therapy was switched to another infliximab biosimilar, infliximab-axxq (Avsola), at the same dosage (5 mg/kg every 8 weeks). Within two months, he experienced recurrent vitreous inflammation and vasculitis confirmed by fluorescein angiography. Following insurer approval, he was reverted to infliximab-dyyb, resulting in prompt resolution of inflammation within one infusion cycle. He has since remained in remission for three years on infliximab-dyyb, with sustained 20/20 visual acuity bilaterally.

CONCLUSION AND IMPORTANCE: This report describes, to our knowledge, the first case of a temporal association between a biosimilar-to-biosimilar switch and disease relapse in a single patient with ocular inflammatory disease. While biosimilars undergo rigorous regulatory testing to confirm clinical equivalence to the reference product, subtle molecular or formulation variations, such as glycosylation or excipient differences, may influence immunogenicity and drug bioavailability in individual patients. As anti-VEGF biosimilars enter into ophthalmic use, clinicians should exercise vigilance during mandated switches, ensuring close monitoring for relapse. Individualized management and open insurer communication are critical to maintaining disease control and optimizing patient outcomes.