The doctrine of equivalents is a legal rule in patent law whereby a party can be liable for infringement even though the party does not literally or precisely infringe every limitation of a patent claim. In 1948, Judge Learned Hand described this as needed “to temper unsparing logic and prevent an infringer from stealing the benefit of the invention”. Royal Typewriter Co. v. Remington Rand, Inc., 168 F.2d 691, 692 (2d. Cir. 1948). The doctrine is applied in a variety of jurisdictions including in the United States.
The current U.S. law is based on the legal test articulated in Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17 (1997), which asks whether the difference is insubstantial, (“substantially the same function in substantially the same way to obtain the same result”, quoting Winans v. Denmead, 15 How. 330, 344 (1854)). Importantly, later cases involve limitations of the doctrine to not extend equivalence beyond the definition detailed above. In other words, one can literally infringe a patent claim or can infringe narrowly under the doctrine.
The doctrine came into play in a recent case at the Court of Appeals of the Federal Circuit. In Eli Lilly and Co. v. Hospira Inc. (Fed. Cir. 2019), the Court found that a description of administration of a pharmaceutical, while not literally infringing the articulated method of administering a drug for treating mesothelioma, did infringe under the doctrine. Based on the Court’s analysis, the difference is that the patented method requires use of a salt and the proposed solution includes a dissolved salt, and argued that a dissolved salt is not a salt.
One major question considered in the case was whether the patentee, during the process of obtaining the patent, ceded that a dissolved salt was different from a salt either in the patent’s specification or during the process of overcoming a rejection. In its analysis, the Court found that the patentee had not ceded that content.
It is important for patent applicants to understand that in the process of overcoming a rejection that they avoid ceding any particular portion of the technology of the patent, unless they absolutely need to in order to overcome a rejection. That is, applicants need to recognize that the scope of the subsequent claims can be broadened under the doctrine, so long as they do not provide fodder in their responses to cede the broadened scope. In addition, applicants need to be aware that this situation, while applied to a U.S. patent, can arise consequential to a corresponding foreign application and could be viewed as ceded in the U.S. patent. Consequently, care needs to be taken to assure that all claim amendments, as well as any remarks do not unintentionally reduce scope, even unwritten scope.