Biosimilars in practice: best-practice immunogenicity assessment and switching/interchangeability strategies for pharmacy-led programs.

Wider access to biologic medicines has been made possible by biosimilars, which provide clinically equivalent options at a lower cost. However, robust immunogenicity surveillance and reliable switching and interchangeability pathways are still necessary for real-world use. The "totality of evidence" may be translated into standardized, patient-centered switching and interchangeability pathways that maintain efficacy and safety through pharmacy-led stewardship initiatives. This narrative review was carried out using PubMed/MEDLINE, Embase, Scopus, Web of Science Core Collection, and Google Scholar between 1 January 2019, and 1 December 2025. This review shows that biosimilars and reference biologics are clinically equivalent, and switching typically has no appreciable impact on population-level safety or immunogenicity. However, switching should be supported by a pharmacy-led toolkit that includes risk-stratified immunogenicity testing (event-triggered vs. scheduled), a minimum assay set plus drug levels, and an action algorithm to differentiate PK failure, PD failure, and immune-mediated failure because a small subset of patients may experience clinically significant ADA/NAb-mediated loss of response or tolerability issues. The issue is now to "operate switching safely" rather than "prove switching," since regulatory trends encourage interchangeability and simplify evidence requirements.