FDA finalises streamlined interchangeability pathway for biosimilars: fewer switching studies required

On 11 October 2026, FDA finalised guidance revising the requirements for biosimilar interchangeability designations. The agency will no longer require dedicated switching studies — in which patients alternate between the reference product and the biosimilar — as a standalone condition for interchangeability. Instead, FDA will accept a totality-of-evidence approach using existing comparative pharmacokinetic, efficacy, safety, and immunogenicity data from the biosimilar's original 351(k) approval submission. See the FDA interchangeable biosimilar products page ↗ for the finalised guidance documents.

The previous requirement for dedicated switching studies was a significant regulatory and cost barrier — switching studies typically cost $30–80 million and added 1–3 years to the interchangeability path. As a result, most biosimilars on the US market lacked interchangeable status, requiring prescriber authorisation for pharmacist substitution. With the new pathway, sponsors can seek interchangeability alongside original approval, without additional clinical trials, if comparative PK and immunogenicity data adequately demonstrate switching safety. This is expected to increase the number of interchangeable biosimilars from the current ~30 to over 100 within 3–5 years. Compare: six adalimumab biosimilars received interchangeability designations in October 2026.

An interchangeable biosimilar can be substituted for the reference product by a pharmacist without requiring the prescriber to write a new prescription or authorise the switch — provided the state pharmacy law allows automatic substitution. As of 2026, 47 states and DC allow automatic substitution of interchangeable biosimilars. Non-interchangeable biosimilars are still clinically appropriate (FDA-approved as biosimilar in efficacy and safety), but require prescriber involvement for switching. The FDA biosimilar product information table ↗ lists all products by interchangeability status.

Increased interchangeability will accelerate biosimilar uptake at the pharmacy level — reducing the cost of biologics (adalimumab, etanercept, trastuzumab, bevacizumab, insulin, filgrastim) by enabling competitive substitution. For patients on Medicaid, interchangeable biosimilars facilitate preferred drug list (PDL) placement at lower rebate-adjusted costs. For prescribers, the change means monitoring for immunogenicity responses on switching remains important — pharmacogenomic variability in drug metabolism does not apply to biologics, but immunogenic responses to protein therapeutics are individually variable. See also: generic vs brand drug guide for the parallel small-molecule context.