Dr. Reddy's Laboratories, Ltd., et al. v. Eli Lilly and Company

Under patent law’s “doctrine of equivalents,” a patent holder can allege infringement even when the defendant does not literally practice every element of a patent claim. But if the patent applicant previously narrowed the claim during prosecution to obtain the patent, the general rule for more than 100 years has been that the patent holder cannot use the doctrine of equivalents in litigation to recapture territory between the broader pre-amendment claim and the narrower post-amendment claim. That rule is known as “prosecution history estoppel.” In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), this Court held that prosecution history estoppel does not apply if the patentee can “show that at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.” Id. at 741. A patentee can make that showing in different ways, including by demonstrating that the “the rationale underlying the amendment … bear[s] no more than a tangential relation to the equivalent in question.” Id. at 740. The question presented is whether, under Festo’s “tangential” exception to prosecution history estoppel, patent owners may recapture subject matter they could have claimed in prosecution but did not, by arguing that they surrendered more than they needed to during prosecution to address a rejection by the Patent Office.