Background
John L. Couvaras filed a U.S. patent application claiming a method of reducing hypertension by administering a combination of two well-established classes of drugs: a GABA-A agonist (such as a benzodiazepine) and an angiotensin receptor blocker (ARB). Both drug classes had been used to treat high blood pressure for decades. The purported novelty of Couvaras’s claimed method was its framing around a specific mechanistic claim: the combination increased the release of prostacyclin — a vasodilatory molecule — in systemic blood vessels, thereby improving vasodilation and reducing blood pressure through this specific pathway.
The USPTO’s Patent Trial and Appeal Board (PTAB) affirmed the rejection of the application on obviousness grounds. PTAB reasoned that because both GABA-A agonists and ARBs were individually known to treat hypertension, a skilled artisan would obviously have been motivated to combine them, and the claimed result of increasing prostacyclin release was inherent in the obvious administration of these two known antihypertensive agents. Couvaras appealed, arguing that even if the combination itself was obvious, discovering the previously unknown prostacyclin mechanism was an unexpected result that should overcome the prima facie case of obviousness.
The Court’s Holding
The Federal Circuit affirmed. The court drew a critical distinction between two different types of “unexpected” showings in patent law: (1) unexpected results — where the claimed combination produces an outcome that is better or different than what the prior art would have predicted; and (2) unexpected mechanism of action — where the combination produces a known result but through a newly discovered biological pathway. Only the former can overcome a prima facie obviousness case. The latter cannot.
The court explained that reciting the mechanism through which known compounds achieve a known result cannot overcome obviousness, even if the nature of that mechanism is genuinely surprising. The reason is grounded in inherency doctrine: when a combination of known drugs for a known purpose is obvious, all of the properties of that combination — including its biological mechanisms — are inherent in the obvious combination. A previously unknown mechanism is not patentable subject matter when it is simply a newly discovered explanation for what the obvious combination was already doing. The patentee cannot “claim” the mechanism as if it were the invention when the actual clinical result (reduced hypertension) was already obvious to achieve.
Key Takeaways
- Discovering an unexpected or previously unknown mechanism of action does not overcome an obviousness rejection when the combination of known compounds achieving a known result was itself obvious.
- Inherency doctrine means that all properties of an obvious combination — including unstudied or newly discovered biological mechanisms — are inherent in that combination and not separately patentable.
- To overcome obviousness with unexpected results, the patentee must show that the combination produces an outcome that is better or different than what a skilled artisan would have predicted — not merely that the reason the expected outcome occurs is surprising.
- Pharmaceutical patent applicants should focus claim language on new therapeutic uses, novel formulations, or patient populations not previously treated — not on mechanistic explanations of why known treatments work.
Why It Matters
This decision has significant implications for pharmaceutical and biotech patent strategy. Drug development often produces valuable scientific insights into how established molecules work — researchers may discover that a combination of drugs achieves its known effect through a novel biological pathway, a finding that has real scientific value and clinical significance. But this decision makes clear that such mechanistic discoveries, by themselves, do not create patentable subject matter if the drugs’ combined therapeutic effect was already predictable.
The ruling creates a practical challenge for companies seeking to protect research investments in mechanism-of-action studies. Companies that invest substantial resources in understanding why a drug combination works may find that they cannot obtain meaningful patent protection for those insights if the clinical outcomes were predictable before the mechanism was understood. The decision encourages inventors to direct their patent applications toward genuinely novel and non-obvious applications — treating a new disease, achieving a different dosing profile, or treating a patient population not previously treated — rather than toward newly explained mechanisms for achieving already-known therapeutic results. For drug combination patents specifically, the bar set by this decision reinforces the importance of building experimental records that demonstrate surprising clinical or pharmacological outcomes, not just surprising scientific explanations.