In a rare move, the Court of Appeals for the Federal Circuit (CAFC) recently reversed its previous ruling for Novartis Pharmaceuticals Corp, now holding that a negative limitation in the claims of Novartis’ patent lacked written description, in Novartis Pharms Corp v Accord Healthcare (Fed Cir, June 21, 2022).

Previously, in a precedential January 2022 decision, the CAFC affirmed the United States District Court for the District of Delaware holding that the patent for Novartis was not invalid and was infringed by HEC Pharm Co.

Upon granting a request for rehearing, the CAFC vacated its precedential January 2022 decision, and reversed the district court’s judgment that Novartis’ claims are not invalid for inadequate written description. In its most recent precedential decision in June 2022, the CAFC raised the standard for demonstrating adequate written description for negative claim limitations by requiring that the limitation in question be “necessarily excluded” in the specification.

Negative limitations

Title 35 USC § 112(a) requires that “the specification shall contain a written description of the invention, and of the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same, and shall set forth the best mode contemplated by the inventor or joint inventor of carrying out the invention.”

This creates two separate requirements referred to as enablement and written description. The specification must describe the invention such that a person having ordinary skill in the art would understand that the inventor actually possessed the invention claimed and the specification must sufficiently disclose how to make and use the invention. Ariad Pharms v Eli Lilly & Co (Fed Cir, 2010) (en banc).

Typically, a claim defines an invention by what it is, rather than by what it is not. In other words, the invention is described by “positive limitations” to define the elements of the claim. However, US patent laws allow for “negative limitations” to be used in drafting a claim. A simple example of a negative limitation would be “wherein the solvent is not water.” The negative limitation is an express exclusion of an element as a feature of the claim. In essence, a negative limitation defines the invention by what it is not.

The patent being challenged is US patent No. 9187405 (the ‘405 patent), owned by Novartis, and is directed to methods of treating relapsing-remitting multiple sclerosis using the immunosuppressant fingolimod. Novartis markets a drug product covered by the patent under the brand name ‘Gilenya’. HEC filed an abbreviated new drug application (ANDA) with the US Food and Drug Administration seeking approval to market a generic version of Gilenya, which triggered Novartis to sue HEC in district court, asserting that HEC infringes the ’405 patent.

Claim 1 of the ‘405 patent recites, “A method for reducing or preventing or alleviating relapses in relapsing-remitting multiple sclerosis in a subject in need thereof, comprising orally administering to said subject 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol, in free form or in a pharmaceutically acceptable salt form, at a daily dosage of 0.5 mg, absent an immediately preceding loading dose regimen.” The limitation of “at a daily dosage of 0.5 mg, absent an immediately preceding loading dose regimen” was added to the claim during prosecution and is the negative limitation at issue.

The district court held that HEC infringes the patent and that the patent is not invalid, finding that the limitation of “at a daily dosage of 0.5 mg, absent an immediately preceding loading dose regimen” met the written description requirement.

HEC appealed that decision to the CAFC, which subsequently affirmed the judgment of the lower district court in January 2022. The CAFC granted the rehearing, and vacated the January 2022 decision, holding that the district court clearly erred in holding that the negative limitation is supported by the written description of the specification.

Silence is inadequate

In arriving at the reversal, the court noted that the ’405 specification does not discuss the presence or absence of a loading dose. Because of this silence, the court takes the position that this does not support the negative limitation that precludes loading doses. In the court’s view, the issue is whether the specification precluded the use of a loading dose. On this, the court finds that the evidence is lacking to demonstrate that a person having ordinary skill in the art would understand that the silence regarding the loading dose in the specification would “necessarily exclude” a loading dose.

The majority states that “If it were, then every later-added negative limitation would be supported so long as the patent makes no mention of it. 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.”

For the first time, the court finds that for an element to be excluded from the scope of a claim via a negative limitation, the specification must “necessarily exclude” the element.

In his dissent, Judge Linn takes the position that the majority elevated the written description standard to require not only a “reason to exclude” but also a showing that the negative limitation is “necessarily excluded”.

Judge Linn’s perspective is that requiring that the limitation be necessarily excluded goes too far. In relying on Ariad, Judge Linn points out that the standard for a negative limitation is no different than for a positive limitation, in that the written description must reasonably convey to those skilled in the art that the inventor had possession of the claimed subject matter as of the filing date of the application.