Interchangeable biosimilars in the United States

What interchangeable means

In the United States, a biosimilar can be given an extra designation: interchangeable. It means a pharmacist can substitute the biosimilar for the reference product without asking the prescriber, in the same way a generic drug is substituted, subject to state law. No other country has this label. In Europe, all approved biosimilars are considered interchangeable in principle, and each country decides on substitution.

How the designation is granted

At first, FDA asked for a study in which patients switched back and forth between the biosimilar and the reference product. That is no longer generally required, and most recent designations have been granted on the same laboratory and pharmacokinetic evidence as the biosimilar licence itself. About half of the biosimilars designated in the last two years received the label on the day they were approved.

Exclusivity

The first product designated interchangeable for a given reference product gets a period of exclusivity, during which FDA will not designate another. Once it expires, later products can be designated, which is why adalimumab and denosumab now have many interchangeable biosimilars while the first ones had the label alone for a year or more. The expiry dates are in the table below.