Drs Kaddis and Oskouei define interchangeable biosimilars, their FDA requirements, and switching studies.
Atheer Kaddis, PharmD: The topic of interchangeability regarding biosimilars is quite complex. Interchangeability is described in the Biologics Price Competition, and Innovation [BCPI] Act  passed by Congress. And at a high level, basically, the Act describes therapeutic interchangeability as having the same clinical result when a biosimilar is administered to a patient as the reference brand would have had, and that a patient can switch back and forth between the reference brand and the biosimilar without having any negative clinical or safety impact by doing so. This means that when a pharmaceutical manufacturer is submitting data to the FDA to obtain interchangeability designation, they have to run clinical trials, with actual patients, to demonstrate what's in the [BCPI] Act.
Now, in regard to actual switching from a reference brand to a therapeutically interchangeable biosimilar, that rule is made by individual states, in the United States. So, in addition to the FDA determining that a product can receive interchangeability, the actual states on an individual level then determine whether providers within that state can substitute a biosimilar for a reference brand. And when it's an interchangeable biosimilar, the provider that's prescribing the drug does not have to write a new prescription for the drug. It can automatically be substituted by a pharmacy, to have the patient receive the biosimilar instead of the reference brand.
Sonia T. Oskouei, PharmD, BCMAS, DPLA: An FDA designation of interchangeability is actually unique to the US, and this is a regulatory term that's important to know. So, per the FDA, a biosimilar candidate can achieve interchangeability typically with the submission of additional data. There's FDA guidance for interchangeability that recommends switching studies be conducted between the originator biologic and a biosimilar where you switch back and forth 3 times at least to show no differences in outcomes. And it's really through the submission of additional data that the FDA would evaluate the biosimilar candidate for interchangeability designation. Now, I say typically because this is not consistent across all molecules in that the FDA actually put out specific guidance for insulins saying that those switching studies may not be necessary for the designation interchangeability for insulin, which really makes sense given this is a century-old product and a much, I would say, less complex biologic. But for the most part, the interchangeably designation is achieved through submission of additional data, which is again, important to note that interchangeably designation is not a clinical designation, meaning an interchangeable biosimilar is not approved as a superior biosimilar from a clinical performance standpoint compared to one that does not have the designation.
Transcript edited for clarity.