Biosimilar
A biological product highly similar to an approved reference product with no clinically meaningful differences in safety, purity, or potency. Biosimilars require more rigorous approval than generic drugs because biological molecules cannot be exactly replicated. Somatropin biosimilars have introduced price competition.
Technical Context
Biosimilar development follows a stepwise approach (totality of evidence): (1) Extensive analytical characterisation (structural comparison using X-ray crystallography, mass spectrometry, chromatography — demonstrating molecular similarity at primary, secondary, tertiary structure and post-translational modifications), (2) Functional assays (receptor binding, cell-based activity assays), (3) Animal studies (PK/PD comparison, sometimes toxicology), (4) Clinical PK/PD study (demonstrating similar pharmacokinetics and pharmacodynamics), and (5) At least one clinical efficacy/safety trial (comparative study demonstrating no clinically meaningful differences). For somatropin biosimilars, analytical and clinical comparability has been demonstrated for several products, introducing price competition. The FDA Purple Book and EMA's biosimilar register list approved biosimilar products. Interchangeability (pharmacy-level substitution without prescriber intervention) requires additional switching studies beyond standard biosimilar approval.