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Biosimilar Interchangeability

An FDA designation under BPCIA allowing a biosimilar to be substituted for the reference biologic at the pharmacy without prescriber consultation, requiring additional switching studies.

How It Works

Interchangeability is a higher FDA standard than basic biosimilarity, created by BPCIA 2010 at 42 U.S.C. 262(k)(4). To earn interchangeable designation, a manufacturer must demonstrate that switching between the biosimilar and the reference product presents no additional risk compared to staying on the reference product. This typically requires dedicated switching studies showing equivalent pharmacokinetics, efficacy, and safety after multiple switches. An interchangeable biosimilar can be substituted by a pharmacist at the counter without calling the prescriber, subject to state pharmacy substitution laws (which vary, some require prescriber or patient notification within 5 business days). The first U.S. interchangeable biosimilar was Semglee (insulin glargine, interchangeable with Lantus) in July 2021. Cyltezo (adalimumab-adbm) received interchangeable designation against Humira in October 2021 and launched with interchangeable status in July 2023. As of 2024 roughly 10 biosimilars have interchangeable designations. FDA proposed in 2024 guidance that switching studies may not be necessary in all cases, potentially streamlining future interchangeable approvals, particularly for protein products where analytical comparability is robust. Importantly, non-interchangeable biosimilars can still be prescribed and dispensed, just not substituted at the pharmacy counter without prescriber authorization; many prescribers specify biosimilars directly on new prescriptions, which achieves similar market effect. The Purple Book indicates interchangeable designations. Interchangeability is one of the primary levers expected to accelerate biosimilar uptake through 2027-2030 as more reference biologics face biosimilar competition.

Related Terms

  • Biosimilar, A biologic product that is "highly similar" to an already approved reference biologic, with no clinically meaningful differences in safety, purity, or potency.
  • Biologic Drug, A complex medication derived from living cells, including monoclonal antibodies, vaccines, and cell therapies, that treats serious conditions like cancer and autoimmune diseases.
  • Reference Product, The FDA-licensed biologic against which a biosimilar is compared and approved under BPCIA, equivalent to the brand-name innovator biologic.
  • Generic Drug, A medication that contains the same active ingredient, dosage, and form as a brand-name drug, approved after the original's patent expires, typically costing 80-95% less.

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About This Definition

This definition is part of the DrugPrice Drug Pricing Glossary, 49 terms explaining how prescription drug pricing works in the United States. All definitions are written in plain language for patients, caregivers, journalists, and healthcare professionals.

this entity is one of the U.S. Medicare prescription-drug pricing concepts that recurs across this site. The definition above is the technical answer; the paragraphs below add the practical context for how the concept connects to the CMS Medicare Part D Drug Spending data data behind every per-entity page on the site.

In the CMS Medicare Part D Drug Spending data data, this concept shapes one or more of the fields that drive the per-entity grades and rankings on this site. The methodology page describes which fields feed into which output; this glossary entry documents the underlying term.

Source: CMS Medicare Part D Spending, 2026.