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In Prometheus Laboratories, Inc. v. Roxane Laboratories, Inc.,[1] a recent decision involving methods of treating a specific subset of patients, the Court of Appeals for the Federal Circuit (“Federal Circuit”) ruled that, although the claims of the patent at issue were invalid as obvious, singling out a particular subset of patients for treatment can still be a valid claiming strategy.

Prometheus Laboratories, Inc. (“Prometheus”), is the owner of U.S. Patent No. 6,284,770 (the ‘770 patent), which is directed to methods of treating a diarrhea-predominant female IBS patient using alosetron (marketed as Lotronex®). Claim 5 of the ‘770 patent, which was amended by Prometheus during a self-requested ex parte reexamination, recites:[2]
<ol start="5">
	<li>A method for treating a diarrhea-predominant female IBS patient, while excluding those with predominant constipation, said method comprising:</li>
</ol>
assessing whether said diarrhea-predominant female IBS patient has experienced symptoms for at least six months; and
administering an effective amount of alosetron or a pharmaceutically acceptable derivative thereof to said patient who has experienced symptoms for at least six months, wherein said effective amount is dependent on the condition of the patient and is at the discretion of the attendant physician.[3]
In 2011, Prometheus filed suit against Roxane and Cipla, alleging infringement of reexamined claims 5, 6, 10, 13, and 14. The suit against Roxane was based on Roxane’s 2009 Abbreviated New Drug Application (“ANDA”) seeking approval of generic Lotronex®. Prometheus alleged that Roxane’s label would encourage doctors to prescribe alosetron in an infringing manner. Cipla was sued for manufacturing the active ingredient in Roxane’s product.

The district court ruled that the asserted claims of the ‘770 patent would have been obvious at the time of the earliest priority date.[4] In reaching its decision, the district court found, and the parties agreed, that the claims of the ‘770 patent are directed to a species within a genus claimed in an earlier, but expired, patent owned by Prometheus – U.S. Patent No. 5,360,800 (the ‘800 patent).[5] In particular, whereas the ‘800 patent claims a method of treating IBS with alosetron, the ‘770 patent is directed to treating a subset of those patients who:
<ol>
	<li>are women;</li>
	<li>have diarrhea-predominant IBS (“IBS-D”);</li>
	<li>have experienced symptoms for at least six months; and</li>
	<li>have had moderate pain.</li>
</ol>
The district court found that it would have been obvious to one skilled in the art to: a) treat women as a separate group of IBS patients; b) limit the patient population to those with IBS-D; c) treat, as a separate group, patients having symptoms for more than six months; and d) target patients with at least moderate pain. The district court further ruled that secondary considerations were not enough to overcome the obviousness determination. For example, regarding commercial success, the evidence suggested that the success was due to Prometheus’s marketing, pricing, and use of rebates, as opposed to the claimed methods.

The Federal Circuit affirmed the district court’s obviousness determination, holding that there was sufficient evidence to establish that it would have been obvious for one skilled in the art “to separately treat the limited subset claimed in the ‘770 patent with alosetron, and that any unexpected results were attributable to factors exogenous to the ‘770 patent.”[6] In making this ruling, however, the Federal Circuit cited previous decisions that held that a species is not necessarily rendered obvious by the genus. Additionally, regarding claims directed to the treatment of a specific subset of patients, the Federal Circuit stated that:

Singling out a particular subset of patients for treatment (for example, patients with a particular gene) may reflect a new and useful invention that is patent eligible despite the existence of prior art or a prior art patent disclosing the treatment method to patients generally. An obviousness rejection likely would not be appropriate where a new patient subset displayed unexpected results.[7]

Thus, although under the specific facts of Prometheus Laboratories, Inc. v. Roxane Laboratories, Inc., the claims reciting methods of treating a specific subset of patients were found to be obvious, the Federal Circuit confirmed that, under different facts, such claims are likely to be considered valid.

[1] Prometheus Labs, Inc. v. Roxane Labs, Inc., No. 2014-1634, 2015 WL 6875218 (Fed. Cir. Nov. 10, 2015).

[2] Claim 5 of the ‘770 patent, which issued on September 4, 2001, recited “[a] method of treatment of diarrhea-predominant female IBS which comprises administering an effective amount of alosetron or a pharmaceutically acceptable derivative thereof.” Following issuance, Prometheus requested ex parte reexamination of the ‘770 patent, and on October 19, 2010, a reexamination certification issued, with amended claim 5 and 6 and new claims 10-16 (claims 1-4 and 7-9 were canceled).

[3] U.S. Patent No. 6,284,770 Cl at 1:23-35 (language added in re-examination italicized).

[4] The district court also found the ‘770 patent invalid for obviousness-type double patenting in light of the claims of the ‘800 patent. The Federal Circuit did not address this issue.

[5] The ‘800 patent was determined by the district court to be prior art to the ‘770 patent.

[6] Prometheus Labs, Inc., 2015 WL 6875218, at *5.

[7] Id.

Methods of treating a subset of patients are likely nonobvious if the subset exhibits unexpected results