Definitions
Biosimilar
A biological medicine that is highly similar to an already approved reference biologic, with no clinically meaningful differences in efficacy, safety, or immunogenicity.
Reference (originator) biologic
The original biological medicine that has been approved based on full clinical development and serves as the comparator for biosimilar evaluation.
Totality of evidence
The comprehensive package of analytical, non-clinical, and clinical data required to demonstrate biosimilarity, rather than reliance on large efficacy trials alone.
Immunogenicity
The ability of a biologic or biosimilar to trigger an immune response, including the development of anti-drug antibodies, which may affect treatment safety or effectiveness.
Switching
The clinical practice of transitioning a patient from a reference biologic to a biosimilar (or between biosimilars) while maintaining comparable efficacy and safety.
Natalizumab
A high-efficacy monoclonal antibody used in multiple sclerosis that blocks α4-integrin, limiting immune cell migration into the CNS but associated with a risk of PML.
Progressive Multifocal Leukoencephalopathy (PML)
A rare but potentially fatal opportunistic brain infection caused by reactivation of the JC virus, primarily associated with natalizumab treatment.
JC Virus (JCV) Index
A quantitative antibody measure used to stratify PML risk in patients treated with natalizumab.
Nocebo effect
A negative treatment response driven by patient expectations or beliefs rather than pharmacological differences, particularly relevant during biosimilar switching.
