Background
Endo Pharmaceuticals owns U.S. Patent No. 8,808,737, which covers a method of treating pain in patients with impaired kidney function using oxymorphone—the active ingredient in Endo’s branded product Opana ER. Oxymorphone is an opioid analgesic, and its metabolism is affected by kidney (renal) function: patients with impaired kidneys cannot clear the drug as efficiently, so they accumulate higher blood concentrations from a given dose. Without dosage adjustment, such patients face increased risks of adverse effects.
The patent claimed a specific method: administering oxymorphone to a renally impaired patient while testing kidney function and then adjusting the dose based on those test results. When Teva filed an ANDA to market a generic version of Opana ER, Endo sued for infringement. The District Court for the District of Delaware dismissed the case under 35 U.S.C. § 101, concluding that the patent was directed to the natural law that oxymorphone concentrations are higher in renally impaired patients—a natural phenomenon—and lacked an inventive concept. Endo appealed.
The Court’s Holding
The Federal Circuit reversed. Writing for a unanimous panel, Judge Lourie held that while the relationship between renal function and oxymorphone levels is indeed a natural phenomenon, Endo’s patent claims did not merely observe or describe that relationship—they claimed an application of it. Specifically, the claims required using the information from kidney function tests to actually change the oxymorphone dose administered to the patient. That active treatment step, the court held, takes the claims outside the scope of an abstract natural law.
Applying the Mayo/Alice two-step framework, the court found at step one that the claims were directed to a specific method of treatment for specific patients using a specific compound at specific doses to achieve a specific outcome—not to a natural law itself. At step two, the court found the specific dosing protocol and the treatment of a defined patient population constituted an inventive application, not just a routine observation of nature. The court distinguished the case from earlier diagnostic-only cases like Mayo v. Prometheus, where the claims were invalid because they told the clinician to observe a natural phenomenon and “apply it” with nothing more than routine mental or conventional steps.
Key Takeaways
- Method of treatment claims that apply a natural phenomenon by requiring specific treatment steps—such as adjusting dosage based on patient-specific test results—are patent eligible under § 101, even if the underlying scientific correlation is a natural phenomenon.
- The key distinction from Mayo is that the Endo claims did not merely direct the practitioner to observe a natural relationship and apply conventional steps; they required an affirmative treatment step (dosage adjustment) that changed patient care.
- Personalized medicine claims that tie a specific treatment protocol to measurable patient characteristics (like kidney function or biomarkers) have a stronger path to eligibility than purely diagnostic claims that stop short of a treatment step.
- Generic companies seeking to invalidate Hatch-Waxman § 101 claims cannot rely on Mayo alone when the patent claims an active treatment method rather than a diagnostic correlation.
Why It Matters
The pharmaceutical industry has increasingly moved toward personalized medicine—tailoring drug dosing and treatment based on a patient’s individual biology, genetics, or physiological characteristics. This decision provided important guidance on when such personalized treatment methods are patent eligible. By drawing a sharp distinction between claims that merely observe a natural correlation (ineligible) and claims that use that correlation to change what a doctor does to the patient (eligible), the Federal Circuit mapped out a viable path for innovators developing precision medicine therapies.
The ruling also had immediate practical consequences: it allowed Endo to continue enforcing its Opana ER patent against Teva’s generic, at least through the § 101 gate. More broadly, the decision, alongside companion rulings like Natural Alternatives International v. Creative Compounds (also decided in 2019), signaled that treatment-focused pharmaceutical claims need not fall victim to the broad logic of Mayo—a welcome development for drug innovators who rely on patent protection to recoup research investments in specialized dosing and patient-selection technologies.