Background
Corcept Therapeutics markets Korlym (mifepristone) for the treatment of hyperglycemia in adult patients with endogenous Cushing’s syndrome who have type 2 diabetes or glucose intolerance. Mifepristone is metabolized in part by the enzyme CYP3A4, and when patients take mifepristone together with a strong CYP3A inhibitor (a drug that blocks that enzyme), the concentration of mifepristone in the blood rises significantly.
Corcept obtained a patent — U.S. Patent No. 10,195,214 — covering a method of treating Cushing’s syndrome by reducing the mifepristone dose to 600 mg per day when co-administered with a strong CYP3A inhibitor, for patients who had previously been stable on 900 or 1,200 mg per day. This specific dosage relationship was derived from Corcept-conducted clinical trials required by the FDA to evaluate the drug-drug interaction.
Teva filed an inter partes review (IPR) petition challenging the patent as obvious, arguing that the prior art would have motivated a skilled artisan to adjust the mifepristone dose when co-administered with a CYP3A inhibitor and that such an adjustment would have been obvious. The PTAB disagreed and upheld the patent. Teva appealed to the Federal Circuit.
The Court’s Holding
The Federal Circuit affirmed. Writing for the court, Judge Lourie held that Teva failed to demonstrate a reasonable expectation of success for the specific dose claimed — 600 mg mifepristone per day when co-administered with a strong CYP3A inhibitor. While the prior art might have suggested adjusting the mifepristone dose in some way when CYP3A inhibitors were present, the court found there was no reasonable basis in the prior art to expect that 600 mg specifically would be a safe and effective dose for the co-administration regimen. The general teaching to reduce a dose does not provide a reasonable expectation of success for any particular dose.
The court reaffirmed a key principle in pharmaceutical patent law: for a dosage claim to be obvious, the prior art must give a skilled artisan a specific reason to arrive at the claimed dose with a reasonable expectation that the claimed dose would achieve the claimed result. An “obvious to try” argument — picking a specific number from a range of possible doses — is insufficient without evidence that the skilled artisan would have been motivated to select that particular value and would have expected it to work as claimed.
Key Takeaways
- Pharmaceutical dosage claims require an obviousness challenger to show a reasonable expectation of success for the specific claimed dose, not merely for adjusting dosage generally.
- “Obvious to try” arguments are weak when the prior art presents a range of possible doses without pointing toward any specific value.
- FDA-required clinical trial data that reveals an unexpected or precisely calibrated dosage relationship can provide strong support for patentability, even when the general concept of a drug interaction was known.
- IPR petitioners challenging dosage-specific pharmaceutical patents must present evidence or expert testimony establishing why a skilled artisan would have expected the specific claimed dose to succeed — not just why some dose adjustment was motivated.
Why It Matters
Teva v. Corcept reinforces a durable principle in pharmaceutical patent law: the road to obviousness runs through specifics, not generalities. Generic manufacturers challenging dosage-specific patents cannot simply argue that skilled artisans would have known to adjust a dose when a pharmacokinetic interaction was present. They must show why a skilled artisan would have landed on the claimed dose in particular and expected it to work.
This decision has practical significance for originators who invest in FDA-required clinical studies on drug-drug interactions. Those studies often reveal specific dosing thresholds or adjustments that can be patented, and the Federal Circuit’s strict reasonable-expectation-of-success standard provides meaningful protection for such claims against IPR challenges. For generic companies, it signals that overcoming dosage claims requires more than pointing to general pharmacokinetic principles — it requires direct evidence tied to the specific numbers the patent recites.