Unless the FDA has designated a biosimilar as interchangeable, it is not eligible for substitution at the pharmacy. While generic drugs can be substituted by a pharmacist for their brand equivalents, the same is not true for biosimilars. Only biosimilars that have undergone additional analysis and, subsequently, have been determined by the FDA to be “interchangeable,” can be readily substituted by a pharmacist without the intervention of the prescriber. So far, the FDA has not designated any biosimilars to be interchangeable to its reference product.^1,2

A manufacturer of a proposed interchangeable product must show the product is biosimilar to a reference product and that it can be expected to produce the same clinical result as the reference product in any given patient.²

The FDA has issued draft guidance for demonstrating interchangeability. For a biosimilar administered more than once to an individual, the manufacturer must show that the risk (in terms of safety or diminished efficacy of alternating or switching between use of the product and its reference product) is not greater than the risk of using the reference product without such alternation or switch.²

State law governs whether automatic substitution of a biosimilar is permitted at the pharmacy. In the absence of pharmacy-level permission, substitution is still possible; hospitals, health plans, and pharmacy benefit managers (PBMs) may consider the use of “therapeutic interchange” as the mechanism to substitute a biosimilar for its reference product. Therapeutic interchange is the process of substituting one product for another when both products are expected to produce similar clinical effects and outcomes based on scientific evidence. Many health systems today use therapeutic interchange for a variety of drugs and biologics to lower costs.³

As of October 22, 2018, 45 states and Puerto Rico have passed laws stating that any biological product under consideration for automatic substitution by a pharmacist without the intervention of the prescriber, must first be approved as interchangeable by the FDA.⁴