The Federal Circuit delivered a significant ruling on patent utility requirements in pharmaceutical claims, holding that the phrase "clinically proven effective" cannot render an otherwise anticipated drug treatment method patentable when specific dosages are already disclosed in prior art. The September 23, 2025 decision in Bayer Pharma Aktiengesellschaft v. Mylan Pharmaceuticals Inc. addresses growing concerns about patent "clawback" strategies in the pharmaceutical industry.
Court Rejects Clinical Validation as Patentability Factor
Bayer's U.S. Patent No. 10,828,310 claimed methods for reducing cardiovascular events by administering rivaroxaban (2.5 mg twice daily) and aspirin (75-100 mg daily) "in amounts that are clinically proven effective." Generic manufacturers Mylan, Teva, and Invagen successfully challenged the patent in IPR proceedings, with the Patent Trial and Appeal Board (PTAB) finding the "clinically proven effective" term non-limiting.
The Federal Circuit affirmed the PTAB's decision but through a different analytical framework. Rather than determining whether the phrase was limiting, the court applied the functional relationship test from King Pharmaceuticals v. Eon Labs, concluding that even if limiting, the clinical validation constituted a "functionally unrelated limitation" that could not rescue an otherwise anticipated method from unpatentability.
Functional Relationship Test Prevents Patent Gamesmanship
The court reasoned that clinical proof of efficacy "in no way transforms the process of taking the drug[s]" at the specified amounts and frequencies, emphasizing that "the actual method . . . is the same" regardless of subsequent clinical validation. This approach allowed the Federal Circuit to sidestep complex inherency analysis that had occupied substantial attention in the PTAB proceedings.
Chief Judge Moore articulated the court's policy concern during oral argument, warning against allowing developers to "put [precise dosages] out there and then later come back and say, now I want to claim it even though it's been in the public domain for a very long time" simply by adding descriptive language. To illustrate this concern, she posed a hypothetical claim limitation requiring amounts that had been "voted best new drug of 2026" – a descriptor that, like "clinically proven effective," adds nothing meaningful to the actual treatment method.
Distinguishing Allergan Precedent
The Federal Circuit distinguished its prior decision in Allergan Sales, LLC v. Sandoz, Inc., where "wherein" clauses specifying minimum safety and efficacy requirements were held limiting and relevant to patentability. The key distinction was that Allergan's claims used "open format" language allowing for additional ingredients like solvents, buffers, and preservatives to ensure safety and efficacy.
In contrast, Bayer's "clinically proven effective" limitation was directly tied to specific dosage amounts already particularly claimed (2.5 mg rivaroxaban and 75-100 mg aspirin), with no evidence that "clinically effective" further limited the dosage in any way. The limitation did not provide functional limitations beyond other claim elements.
Implications for Patent Strategy
The decision reveals potential strategies for patent drafters seeking to include clinical efficacy limitations. The court suggested that functional relationships might exist if dosage ranges were broader but clinical effectiveness was proven only for narrower ranges – for example, if aspirin dosage was listed as 50-100 mg but proven effective only for 75-100 mg.
The court also rejected Bayer's evidence of unexpected results because that evidence was tied solely to the "clinically proven effective" limitation, finding no nexus between the clinical results and the claims as a whole.
Balancing Innovation Incentives and Patent Scope
The ruling addresses fundamental tensions in pharmaceutical patent law between providing incentives for clinical development and preventing indefinite extension of patent protection through post-hoc validation. While clinical work provides valuable societal benefits, the court determined it doesn't transform an anticipated method into a patentable one when prior art already disclosed using the same drugs for the same purpose.
This decision establishes important precedent for evaluating pharmaceutical method claims that include clinical validation language, requiring patent applicants to demonstrate genuine functional relationships between efficacy limitations and claimed methods rather than relying on post-invention validation to confer patentability.
