Per a report in BioCentury, the agency said it will "generally" require switching studies to show interchangeability between any biological products that are dosed more than once. Switching studies should evaluate pharmacokinetic and pharmacodynamic measures as primary endpoints, while also assessing immunogenicity and safety. The agency specified that the studies should include at least three switches between a reference product and proposed biosimilar; the last switch should be a transition to the proposed biosimilar from its reference product.
FDA emphasized that an imbalance in adverse events or immune responses reported at any point during a switching study will "raise concerns" as to the biologics' interchangeability, because it may be difficult to determine which product caused the event. The agency also encouraged powering studies to accommodate patient dropouts, noting that an imbalance in dropout rates may also suggest that compounds are not interchangeable. The agency encouraged companies to first seek a candidate's approval as a non-interchangeable biosimilar if there is "residual uncertainty regarding interchangeability" based on adverse events. The sponsor could then conduct postmarketing studies to show interchangeability.
FDA suggested a two-part study design for sponsors seeking evidence of both biosimilarity and interchangeability. The agency said that after an appropriate measure of clinically meaningful differences between two biologics, a second stage of an integrated study could re-randomize patients into a switching study. The study should be powered to adequately measure both PK and PD, as well as clinical effectiveness.
The guidance said sponsors seeking to extrapolate data supporting interchangeability to additional indications "need to provide sufficient scientific justification" that addresses factors such as immunogenicity risk, PK and mechanism of action.
FDA will accept comments on the draft guidance through March 19. In a Federal Register notice accompanying the guidance, FDA asked stakeholders to address how the agency should consider additional indications approved for a reference product after approval of its interchangeable product, and if the agency should change or add to its comparability assessments for post-approval manufacturing changes of interchangeable products.