In the U.S., a prosecution history of a patent (i.e., the proceedings between the patent applicant and the USPTO from application filing to patent issuance) comes into play in the context of claim construction (for example, before a district court, before the PTAB in a post-grant proceeding, or in the eyes of a third party analyzing the patent for freedom to operate reasons), and also in the context of an assessment of infringement under the doctrine of equivalents.

But the line between the two uses of a patent's prosecution history tends to be blurry. In Part 1 of this series,, we looked at the use of prosecution history in claim construction. Here in Part 2, we discuss its use in a doctrine of equivalents analysis.

Prosecution History in Doctrine of Equivalents Analysis

A prosecution history may limit a range of infringement available under the doctrine of equivalents. Prosecution history estoppel prevents a patentee from using the doctrine of equivalents to recapture subject matter surrendered during prosecution from the literal scope of a claim. See Hoganas AB v. Dresser Indus., Inc., 9 F.3d 948, 950 at n.6 (Fed. Cir. 1993). 

Prosecution history estoppel can arise from a variety of acts taken during prosecution. For example, it is well settled that amendments made in response to prior art rejections can result in prosecution history estoppel. This is frequently called "classical" prosecution history estoppel. Hughes Aircraft Co. v. U.S., 717 F.2d 1351, 1362 (Fed. Cir. 1983); Keystone Driller Co. v. Northwest Eng'g Corp., 294 U.S. 42, 48 (1935). An applicant cannot amend the claims in response to an examiner's rejection and then use the doctrine of equivalents to try to obtain the very same subject matter that was given up to obtain the patent. See Hilgraeve Corp. v. McAfee Assoc., Inc., 224 F.3d 1349 (Fed. Cir. 2000); Sextant Avionique, S.A. v. Analog Devices, Inc., 172 F.3d 817, 819 (Fed. Cir. 1999); Loral Fairchild Corp. v. Sony Corp., 181 F.3d 1313 (Fed. Cir. 1999); Chemical Eng'g Corp. v. Essef Indus., Inc., 795 F.2d 1565 (Fed. Cir. 1986).

Estoppel may also be created by arguments and representations made to the USPTO to obtain allowance of a patent, even without a claim amendment. Andersen Corp. v. Fiber Composites LLC, 474 F.3d 1361 (Fed. Cir. 2007). This is where the line becoming blurry with claim construction is most noticeable. Unmistakable assertions to the USPTO in support of patentability, whether or not they were required to secure allowance of the claims, will estop the patentee from obtaining protection of the subject matter surrendered via the doctrine of equivalents. Athletic Alternatives, Inc. v. Prince Mfg., Inc., 73 F.3d 1573, 1582 (Fed. Cir. 1996) (citing Kinzenbaw v. Deere & Co., 741 F.2d 383, 389 (Fed. Cir. 1984)); see also, Amgen Inc. v. Coherus BioSciences, Inc., 931 F.3d 1154 (Fed. Cir. 2019) (Amgen "clearly and unmistakably-and indeed, repeatedly-indicated to competitors that it surrendered processes using combinations of salts different from the 'particular combinations of salts recited in the . . . claims[.]'"); Pharma Tech Sols., Inc. v. LifeScan, Inc., 942 F.3d 1372, 1380 (Fed. Cir. 2019); Abbott Lab'ies. v. Dey, 287 F.3d 1097 (Fed. Cir. 2002); Pharmacia & Upjohn Co. v. Mylan Pharms., Inc., 170 F.3d 1373 (Fed. Cir. 1999); Bai v. L&L Wings, Inc., 160 F.3d 1350, 1356 (Fed. Cir. 1998); Insituform Techs., Inc. v. CAT Contracting, Inc., 99 F.3d 1098, 1108-09 (Fed. Cir. 1996).

The Federal Circuit stated that representations made to foreign patent offices may also be considered in determining the applicability of prosecution history estoppel.  "[R]epresentations to foreign patent offices should be considered . . . when [they] comprise relevant evidence." Caterpillar Tractor Co. v. Berco, S.p.A., 714 F.2d 1110, 1116 (Fed. Cir. 1983). A court will consider statements made in foreign prosecution when:

The statement was made in an official proceeding where the patentee had every incentive to exercise care in characterizing the scope of its invention;

The patents are related and/or share an identical claim; and the statement was not related to unique aspects of foreign patent law.

Apple Inc. v. Motorola, Inc., 757 F.3d 1286, 1312 (Fed. Cir. 2014). See also Tanabe Seiyaku Co., Ltd. v. USITC, 109 F.3d 726 (Fed. Cir. 1997); Merck & Co., Inc. v. Mylan Pharms., Inc., 19 F.Supp.2d 334 (E.D. Penn. 1998).

Prosecution history estoppel resulting from arguments and amendments regarding one claim may be applied to limit the scope of other claims not only in the same patent but also in related patents. Southwall Techs., Inc. v. Cardinal IG Co., 54 F.3d 1570 (Fed. Cir. 1995); Diversitech Corp. v. Century Steps, Inc., 850 F.2d 675 (Fed. Cir. 1988); Builders Concrete, Inc. v. Bremerton Concrete Prods. Co., 757 F.2d 255 (Fed. Cir. 1985). Prosecution history estoppel, however, may not apply to patents issued before the acts that gave rise to the estoppel. See Water Tech. Corp. v. Calco, Ltd., 850 F.2d 660, 667 (Fed. Cir. 1988).


Consider the following suggestions to avoid creating prosecution history that may lead to estoppel in a doctrine of equivalents analysis.

  • Attempt to draft claims that will not have to be amended. This may require a more extensive search of the prior art than was the typical practice. The practice of just drafting a broad claim and then amending it to whatever the examiner will allow may not be a good practice for avoiding prosecution history estoppel.
  • If an amendment is made for a reason unrelated to patentability, explain it explicitly.
  • Avoid amending claims more narrowly than necessary to avoid the prior art. Consider singling out the element to be narrowed.
  • Do not make gratuitous arguments, i.e., arguments that are not necessary to overcome the prior art. Make your amendment more like a targeted "rifle shot" than a "shotgun" approach; consider whether each amendment and argument may create prosecution history estoppel.
  • Try everything before filing an amendment. Examiner interviews, appeals, and arguing against the prima facie case of unpatentability made out by the examiner have now all taken on a heightened importance as you attempt to avoid the rejection without amending the claim. Maybe you can convince an examiner there is no prima facie case of obviousness. Consider all these routes first, in the interest of avoiding having to amend the claim.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.