IP Briefs: The Positive Side of Negative Disclaimers

A new patent application can be rejected over an existing patent that was not publicly available when the new application was filed. Sometimes, this can be resolved by adding a negative disclaimer to the new filing.
Jun 01, 2007
Volume 20, Issue 6

Biopharmaceutical and pharmaceutical companies rely on patent protection of proprietary compounds to ensure an exclusive market position after approval to market the compound. Typically, a company will file a patent application on the compound or on a number of candidate compounds well before clinical studies begin, and sometimes before a single compound is identified for clinical development.

When preparing an application for filing, the company's patent attorney conducts a search of the patent and scientific literature, to evaluate whether the candidate compounds have already been described in the literature, and are thus unpatentable. As any patent attorney will admit, however, it is impossible to identify every possible document that may bear on patentability of the candidate compounds for two reasons. First, no search can be exhaustive of the patent and scientific literature worldwide. Second, most patent applications are published 18 months after filing with the US Patent and Trademark Office. This means that a patent publication that may render one or more of the company's candidate compounds unpatentable for lack of novelty may not be publicly available at the time the patent attorney conducts the patentability search and files the company's patent application. Thus, short of having a crystal ball, any assessment of patentability is imperfect.

Years after filing the patent application, a patent examiner will be assigned to the application to opine on the patentability of the pending claims. The patent examiner will conduct a search of the scientific and patent literature, which will now include patent application publications that were not yet published when the patent attorney conducted the patentability search years before, i.e., patent applications filed before, but published after, the filing date of the company's patent application. If a patent publication is identified by the examiner that describes one or more of the claimed candidate compounds, the applicant is faced with an unpleasant surprise—any pending claims that include a compound described in the newly identified publication are deemed unpatentable for lack of novelty.

This article considers the use of a tool called a negative disclaimer, or more simply, a disclaimer, as an approach for dealing with these unexpected surprises. We review the admissibility of disclaimers in the US and in Europe as a means to restore novelty to a claim rejected over a document that was not publicly available, or was unknown to the patent attorney at the time of filing the patent application.


Consider the claims in US Patent No. 6,989,366. Claim 1 is to a method for reducing food intake in a subject desirous or in need of reducing food intake. The method involves administering an amount of an exendin agonist effective to reduce food intake, wherein the exendin agonist is an exendin peptide analog. Claim 15 specifies that the exendin agonist is an exendin peptide analog having a certain generic sequence, with the proviso that the exendin peptide analog is not exendin-3 or exendin-4. The language set forth in italics is a disclaimer and has the effect of excluding from the scope of the claim the peptides known as exendin-3 and exendin-4.


The concept of using a negative disclaimer in a claim to distinguish over the prior art first appeared in the US legal system over 30 years ago.1 In a chemical case before the court, a pending claim had been amended to recite "said homopolymer being free from the proteins, soaps, resins, and sugars present in natural Hevea rubber" in order to exclude previously disclosed elements in the art. The court found the disclaimer permissible, because each recited limitation in the disclaimer was definite. In another case,2 the court found that the negative disclaimer "incapable of forming a dye with said oxidized developing agent" was definite because the boundaries of the patent protection sought were clear.

In these cases, the literal words used in the negative disclaimer were not present in the application as filed. Addition of a disclaimer to a claim based on words not present in the application as filed is referred to as an undisclosed disclaimer.

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