Cornell Journal of Law and Public Policy


Reasonable interchangeability, Eisai v. Sanofi-Aventis


This Note posits that a single product with multiple, non-reasonably interchangeable use cases can function like multiple products, exchanged in multiple product markets, for purposes of assessing antitrust liability.

In antitrust law, individual product markets are defined by the principle of reasonable interchangeability (or substitutability). Where a single product has multiple uses that are not reasonably interchangeable, the use cases should define the product market. The lay concept of what constitutes a single product is not applicable to antitrust law when a single product has multiple, non-reasonably interchangeable use cases. As a result, antitrust liability should attach where a seller leverages market power in a unique use case of one product to foreclose competition in another use case of the same product.

I use the recent Third Circuit case Eisai v. Sanofi-Aventis, in which plaintiff Eisai alleged that defendant Sanofi improperly leveraged market power in a unique FDA-approved indication (use case) of an anticoagulant drug to coerce more sales in competitive indications, to illustrate my argument.