The Sound of Silence: Claiming Negative Limitations | Kilpatrick Townsend & Stockton LLP

The patent specification must contain a written description of the invention.1 In order to meet the written description requirement, the applicant must notify the skilled person with reasonable clarity that he possessed the invention on the requested filing date.2 But how can a patent specification show the existence of a missing feature, i.e. a “negative restriction”? Does the specification have to explicitly describe the feature and/or lack of the feature? Is silencing the claimed feature sufficient to show support? That’s one of the questions asked at Novartis Pharmaceuticals Corp. against Accord Healthcare, Inc., 21 F.4th 1362 (Fed. Cir. 2022).3

The litigation in the Novartis Pharmaceuticals Corp. v. Accord Healthcare, Inc. addresses the validity of a patent claim with a negative qualification: “Absence of an immediately preceding loading dose regimen.” (“Novartis”). The district court ruled that the claim was valid and that HEC Pharm Co., Ltd.’s abbreviated New Drug Approval (“ANDA”). and HEC Pharm USA Inc. (collectively, “HEC”) infringes the claim.5 HEC appealed to the Federal Circuit, arguing that the claim is invalid for lack of written descriptive support. The Federal Circuit affirmed the District Court’s decision.6

In a decision dated January 3, 2022, the Federal Circuit ruled that the negative limitation “without an immediately preceding loading dose regimen”7 is supported by the specification as filed, although the specification makes no mention of a loading dose, or lack thereof.8 It is noted that the parties have agreed that: (1) a loading dose is greater than the daily dose; (2) a loading dose is usually administered as the first dose; and (3) “Loading doses were well known in the medical field.”9 The Court noted that “the lack of a literal basis in the specification for a negative limitation may not be sufficient to establish prima facie evidence of lack of descriptive support” there the written description can take various forms and newly added claim limitations can be supported by implicit or inherent disclosure.10 The court found that the negative limitation in the Novartis patent is supported by the implicit or inherent disclosure since the specification of the patent was disclosed use of a claimed drug (fingolimod hydrochloride) in an animal model and a “Prophetic Trial” in humans,11 but none of the studies disclosed the use of a loading dose regimen.12 The court agreed with Novartis experts that a pers on by skilled person “would have had the patent as . . . complete document[] that should give you all the information you need to run the claims” and “from the point of view of a skilled artisan that if the Prophetic Trial included a loading dose, the patent would state so explicitly.”13 Although the specification does specify a loading dose or lack thereof, the limitation of “absence of an immediately preceding loading dose” is implicitly disclosed and supported by the application as filed.14

Specifically, throughout the Opinion, the Court reiterated its position that there is no “new and stricter standard for negative claim limitations,”15 citing support from the Court’s precedents: Inphi Corp., 805 F.3d at 1356; Santarus Inc. v. Par Pharmaceutical, Inc., 694 F.3d 1344 (Federal Circ. 2012); Referring to Bimeda Research & Development Ltd., 724 F.3d 1320 (Bund. Cir. 2013); Nike, Inc. v. Adidas AG, 812 F.3d 1326 (Federal Circ. 2016); Inventors’ association UroPep GbR v. Eli Lilly & Co., 276 F.Supp. 3d 629, 657–58 (ED Tex. 2017), aff’d, 739 F. App’x 643 (Fed. Cir. 2018). While “[t]The mere absence of a positive recitation is not one [sic] Basis for an exclusion”16 “[t]The failure of the specification to expressly mention a limitation that later appears in the claims is not fatal if a person skilled in the art, reading the specification, would recognize that the new language reflects what the specification shows that it was invented. 17 The Court emphasized that the disclosure must be read from the perspective of a person skilled in the art, taking into account the context and knowledge of the person skilled in the art, and even common sense in the description and excluding others without explanation, so long as the claim does not indicate to the person skilled in the art that it covers embodiments that are inconsistent with, and therefore not supported by, the disclosure


For patentees who need to defend claims with negative qualifications, this case shows that silence alone is not enough, implicit or inherent disclosures, however, a skilled person’s knowledge and common sense can bring “tone” to the silence and constitute adequate disclosure. Reports or statements by experts can support this position.

For contestants to claims citing negative limitations, it remains true that “[t]The mere lack of a positive recitation is not a basis for disqualification.”20 Additionally, in almost every case of written description, the Federal Circuit affirmed the principle that compliance with the requirement of a written description is an fact-based inquiry that will necessarily vary from case to case will be the nature of the claimed invention.21 Challengers may argue that the nature of the claimed invention is such that the absence of the feature is not readily apparent, either expressly or implicitly from the disclosure.

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