During the prosecution of a patent application before the U.S. Patent and Trademark Office, claim amendments that introduce a negative limitation―the exclusion of a particular element or feature from the scope of the claims―may be dispositive in distinguishing the instant application from the prior art and advance the application toward allowance. However, the introduction of negative limitations may raise questions and issues as to whether the claims satisfy the written description requirement under 35 USC §112(a). Recently, the U.S. Court of Appeals for the Federal Circuit in Novartis Pharmaceuticals Corp. v. Accord Healthcare, Inc., No. 2021-1070, 2022 WL 2204163 (Fed. Cir. June 21, 2022) elaborated upon what satisfies the written description requirement with respect to the recitation of negative claim limitations.

Novartis owns U.S. Patent No. 9,187,405 (’405 patent), which relates to methods for treating relapsing-remitting multiple sclerosis via the oral administration of fingolimod, an immunosuppressant marketed under the name Gilenya. Independent claim 1 recites the “a daily dosage of 0.5 mg [of fingolimod], absent an immediately preceding loading dose regimen.” See ’405 patent, claim 1 (noting claim language added by post-filing amendment in italics). HEC Pharm Co., Ltd. and HEC Pharm USA Inc. (HEC) filed an abbreviated new drug application with the Food and Drug Administration to seek approval for marketing a generic version of Gilenya. Novartis sued HEC, alleging that its generic drug infringes the ’405 patent. In a bench trial, the district court held that HEC did infringe the ’405 patent and found no invalidity with respect to, inter alia, an alleged inadequate written description for the recitation of the absence of a loading dose in the claimed methods of treatment, which was added during prosecution to distinguish it from the cited prior art and obtain allowance. HEC appealed and the Federal Circuit affirmed in a split decision, with Judge Kathleen M. O'Malley and Judge Richard Linn in the majority, and Chief Judge Kimberly A. Moore dissenting. See generally Novartis Pharms. Corp. v. Accord Healthcare, Inc., 21 F.4th 1362 (Fed. Cir. 2022). HEC petitioned for a rehearing. In the meantime, Judge O’Malley retired, and Judge Todd M. Hughes replaced her on the panel for the case, which granted a rehearing. Upon rehearing, Chief Judge Moore authored the majority decision (with Judge Linn dissenting) vacating the prior decision and reversing the district court’s judgment that Novartis’ claims are not invalid due to an inadequate written description.

As part of its new ruling, the Federal Circuit panel noted that the recitation of negative limitation has adequate written description when “the specification describes a reason to exclude the relevant [element].” See Novartis, 2022 WL 2204163, at *2 (quoting Santarus, Inc. v. Par Pharm., Inc., 694 F.3d 1344, 1351 (Fed. Cir. 2012)). For example, a specification could include “statements… expressly listing the disadvantages of using” the excluded element. See id. (quoting Santarus, 694 F.3d at 1351). The specification may also distinguish the excluded element from its alternatives. See id. (citing Inphi Corp. v. Netlist, Inc., 805 F.3d 1350, 1355 (Fed. Cir. 2015)).

Thus, the Federal Circuit concluded that there must be a disclosure in the specification regarding the negative limitation or excluded element, and that silence regarding the excluded element may not constitute a disclosure unless, for example, a skilled artisan would understand that silence necessarily (inherently) discloses the negative limitation. See id. (citing Seabed Geosolutions (US) Inc. v. Magseis FF L.L.C., 8 F.4th 1285, 1288 (Fed. Cir. 2021); Tronzo v. Biomet, Inc., 156 F.3d 1154, 1159 (Fed. Cir. 1998)). The mere absence of a positive recitation is not enough to support the basis for an exclusion, see MPEP § 2173.05(i), such that testimony from a skilled artisan regarding mere probabilities or possibilities that the recited element would be excluded would not suffice to establish a written description. Otherwise, any negative limitation added to the claims during prosecution could be adequately supported based on silence regarding the negative claim limitation in the specification. In other words, “While a negative limitation need not be recited in the specification in haec verba, there generally must be something in the specification that conveys to a skilled artisan that the inventor intended the exclusion, such as a discussion of disadvantages or alternatives.” See Novartis, 2022 WL 2204163, at *2.

The court further elaborated that the disclosure of a negative limitation may be inherent if “a skilled artisan would understand the specification… inherently disclose[s] the negative limitation.” See id. Thus, even if the specification were silent regarding an explicit disclosure of the negative limitation, recognition by a person skilled in the art that silence means the element is necessarily excluded may be enough to satisfy the written description requirement for the negative limitation.

In granting HEC’s request for rehearing, vacating its earlier decision and reversing the determination of the district court, the Federal Circuit panel determined that the specification of the ’405 patent did not disclose or discuss the presence or absence of loading doses. See id. at *3. The court also pointed out that the negative limitation was a later-added limitation to overcome the prior art and such a limitation would not have been necessary if reciting a “daily dosage,” without mention of the loading dose, meant exclusion of the loading dose. See id. at *4. Furthermore, the silence within the specification regarding a loading dose would not lead a person skilled in the art to the understanding that reciting a dosage regimen without the loading dose meant the exclusion of the loading dose. See id.

At the end of the day, the Federal Circuit panel made clear that it was not creating a heightened standard for disclosure of negative limitations. It further reiterated that the threshold for meeting the written description requirement is that the disclosure must only “reasonably convey[ ] to those skilled in the art that the inventor had possession of the claimed subject matter as of the filing date” and that it has not established any new standard for meeting the written description requirement in regard to negative limitations. See id. at *5 (quoting Ariad Pharms., Inc. v. Eli Lilly & Co., 598 F.3d 1336, 1351 (Fed. Cir. 2010) (en banc)). Thus, the “disclosure” required to satisfy the written description requirement is the same for negative limitations as it is for positive limitations. However, at times, silence may be adequate for satisfaction of the written description requirement if a person skilled in the art would understand the negative limitation to necessarily be present.