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Federal Circuit finds genus didn’t anticipate species

April / May 2023 IP Newsletter

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Does the disclosure of a chemical genus render all of the species within it “inherently obvious” and therefore unpatentable? Not always, as the challenger in Mylan Pharmaceuticals Inc. v. Merck Sharp & Dohme Corp. learned.

A salty issue

Merck Sharp & Dohme Corp. (Merck) owns a patent on a type of dihydrogen phosphate salt (sitagliptin DHP) that belongs to a genus of DP-IV inhibitors. Mylan Pharmaceuticals petitioned for an inter partes review (IPR). Under IPR, the Patent Trial and Appeal Board (PTAB) can reconsider and cancel an already-issued patent based on certain types of “prior art” that made the patented invention obvious or anticipated and therefore unpatentable.

Mylan argued that some of the patent claims were anticipated by prior art collectively referred to as “Edmonson.” Edmonson disclosed a genus of DP-IV inhibitors and 33 compounds (or species), including sitagliptin. It also disclosed that pharmaceutically acceptable salts can be formed using “particularly preferred” acids, including phosphoric acid.

The PTAB concluded that Mylan hadn’t established the claims were anticipated or would’ve been obvious at the time Merck’s invention was made. Mylan turned to the U.S. Court of Appeals for the Federal Circuit for relief.

Vision quest

Merck argued that the PTAB was correct to find that Edmonson didn’t inherently disclose its patented salt. The combined list of compounds and acids disclosed in Edmonson would result in 957 salts, some of which might not even form under experimental conditions.

Mylan relied on the “at once envisage” theory. It states that prior art may be deemed to disclose each member of a genus when, reading the prior art, a person of ordinary skill in the field can “at once envisage every member” of the class. The case where the theory originated referred to a limited class and involved a genus of only 20 compounds.

The Federal Circuit said the 957 salts here were a far cry from that narrow genus. And Mylan’s own expert stated that salt formation is an unpredictable art that requires a trial-and-error process.

The court also agreed that Edmondson didn’t expressly disclose the sitagliptin DHP salt. Mylan’s expert stated that nothing in Edmonson directs a skilled artisan to sitagliptin from among the 33 listed inhibitors. Further, Edmonson didn’t single out phosphoric acid or any phosphate salt of any inhibitor, and its list of preferred salts appeared 44 pages earlier.

A question of class

While the court held that the class here didn’t meet the “at once envisage” standard for an invention to be inherently anticipated, it declined to provide a specific number that defines a “limited class.” That figure, the court said, depends on the class.