Federal Circuit ruling marks out dangers of doctrine of equivalents estoppel

While the doctrine of equivalents (DOE) is a powerful tool allowing patentees to prevent accused infringers from skirting liability by merely using an equivalent of a claimed feature, the Federal Circuit’s recent Pharma Tech Solutions Inc v Lifescan Inc decision reiterates the importance of carefully crafting claim amendments and arguments during prosecution to avoid being precluded from enforcing a patent under the DOE. It also provides insights that may be useful when drafting a patent application and/or pursuing continuation applications.

Pharma Tech Solutions accused LifeScan Inc of infringing US Patent No 6,153,069 and its continuation, US Patent No 6,413,411, pertaining to blood glucose monitoring for home use. During litigation, Pharma Tech conceded lack of literal infringement and was required to amend its complaint to specify the precise basis for infringement under the DOE. The district court granted summary judgment of non-infringement under the DOE because of prosecution history estoppel. 

On appeal, the Federal Circuit affirmed that the doctrine of prosecution history estoppel prevented Pharma Tech from using the DOE to recapture subject matter surrendered from the literal scope of the claims during prosecution. Specifically, the court determined that prosecution history estoppel arose through both argument-based estoppel based on arguments made during prosecution and amendment-based estoppel “by making a narrowing amendment to the claims”. While the analysis is highly fact specific, the court provided an in-depth explanation of both types of estoppel. 

Argument-based estoppel requires “a clear and unmistakable surrender of subject matter” and “[t]he relevant inquiry is whether a competitor would reasonably believe that the applicant had surrendered the relevant subject matter”, regardless of whether the argument was required to secure allowance. Narrowing claim amendments “may be presumed to be a general disclaimer of the territory between the original claim and the amended claim” and cause amendment-based estoppel except when: “(1) the equivalent was unforeseeable at the time of the application; (2) the rationale underlying the amendment may bear no more than a tangential relation to the equivalent in question; or (3) there may be some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.”

The analysis of whether an amendment falls under the tangential relation exception focuses on the “objectively apparent reason for the narrowing amendment”. Merely because a claim “amendment may have ceded more claim scope than is necessary to overcome the prior art does not mean that the tangential relationship exception applies …”.

During prosecution of the ’069 patent, the claims were amended in view of cited art to recite obtaining two or more Cottrell current readings, converting these current readings to measure analyte concentration and linearly comparing the analysis concentration measurements. In addition, the inventors argued three times that the prior art did not disclose the amended claims. Pharma Tech conceded that any estoppel in the ’069 patent applied to the ’411 patent. Holding that both types of estoppel bar Pharma Tech’s infringement claims under the DOE, the Federal Circuit brushed aside arguments that limitations added during prosecution fell into the tangential relations exception.

Despite the fact-specific nature of prosecution history estoppel, the Pharma Tech decision provides insights on how to reduce the likelihood of amendment-based and argument-based estoppel during prosecution. The decision also provides insights that may be useful when drafting a patent application and/or pursuing continuation applications.

To avoid amendment-based estoppel, as is obvious, applicants should avoid making claim amendments that are not necessary to overcome the prior art. Since estoppel attaches only to existing claims, applicants should consider backup amendments as new dependent claims. For any claim amendment not specifically relied upon to distinguish the art, the record should establish that the amendment was only tangentially related to patentability, such as to overcome an indefiniteness rejection. Applicants also should consider providing a general statement arguing that the amendment does not result in amendment-based disclaimer, which may reduce the likelihood of such a finding in a subsequent enforcement action.

To avoid argument-based estoppel, applicants should avoid statements that objectively establish a surrender of subject matter. For example, applicants should frame arguments using only the literal claim language rather than generalising or summarising the claim language in order to prevent increased territory being disclaimed. Unless it is necessary, applicants also should avoid repeatedly making similar arguments, as such emphasis could increase the likelihood of prosecution history estoppel. 

Finally, applicants should consider drafting multiple independent claims that cover the technical and commercial advantages of the invention from different angles. In this way, it is unlikely that the same amendments and arguments could be used to preclude the DOE for all of the claims.

While it is best practice to maintain a pending continuation application for commercially valuable technology to allow claims targeted at competitors, for example, it is highly likely that prosecution history from the parent will pass through to the continuation application. To reduce this likelihood, applicants should clarify the record during the prosecution of the parent application and, if possible, include different claim terminology in the continuation application. Claiming the invention differently in parent and continuation applications while strictly arguing the recited claim language during prosecution reduces the likelihood of estoppel reaching subsequent related applications.