The Federal Circuit’s recent decision in United Therapeutics Corp. v. Liquidia Techs., Inc., No. 2022-2217, 2023 WL 4695903 (Fed. Cir. July 24, 2023), provides an interesting discussion on the written description and enablement of method of treatment claims where treatment of a subset of patients may not be safe or efficacious. Claim 1 of U.S. Patent 10,716,793, for example, reads as follows:

1. A method of treating pulmonary hypertension comprising administering by inhalation to a human suffering from pulmonary hypertension a therapeutically effective single event dose of a formulation comprising treprostinil or a pharmaceutically acceptable salt thereof with an inhalation device, wherein the therapeutically effective single event dose comprises from 15 micrograms to 90 micrograms of treprostinil or a pharmaceutically acceptable salt thereof delivered in 1 to 3 breaths.

The Federal Circuit agreed with the district court that the claims cover the treatment of all five groups of pulmonary hypertension (PH). The written description and enablement issue centered on the safety concerns associated with treating patients with group 2 PH. Liquidia’s expert, for example, testified that a skilled artisan would have concerns about administering inhaled treprostinil to patients with group 2 PH because at least one earlier study on those patients failed due to increased mortality. The Federal Circuit, however, affirmed the district court’s ruling that the claims were not invalid for lacking written description or enablement. 

The Federal Circuit noted that under the district court’s claim construction (which was not at issue on appeal), the claims do not import any additional efficacy or safety limitations. Rather, “therapeutically effective dose,” as construed by the district court, means “a dose given in a single treatment session that causes an improvement in a patient’s hemodynamics.” The Federal Circuit agreed that the record showed that patients with group 2 PH exhibit an improvement in hemodynamics, which is all that is required under the district court’s claim construct. 

The Federal Circuit also declined to treat group 2 PH differently from the other four groups of PH, stating, “[i]t would be incorrect to fractionate a disease or condition that a method of treatment claim is directed to, and to require a separate disclosure in the specification for each individual variant of the condition … unless these variants are specified in the claims.” United Therapeutics Corp., 2023 WL 4695903 at *7. According to the Federal Circuit:

Disease-specific treatment requirements are matters for the FDA and medical practitioners. They are best suited to make these determinations because practitioners are informed by the findings of the regulatory agency to avoid treatment of patients who will not properly respond. And every claim to a method of treatment of an ailment has refinements. That is, for any given method of treatment claim, there may be a subset of patients who would not benefit from or should not take the claimed treatment …. That does not mean that such claims are not sufficiently enabled or supported by written description. A subset of unresponsive patients is not analogous to unsupported species in a generic claim to chemical compounds.

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