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The Doctrine of Equivalents in Pharmaceutical Actions

Fish & Richardson

Authors

When a product or process does not literally infringe a patent’s claim language, the doctrine of equivalents (DOE) holds that a competitor’s product or process may still infringe if it is substantially equivalent to the claimed invention.1 The DOE is especially advantageous in the pharmaceutical industry, where a generic drug may avoid literal infringement but function in substantially the same way to achieve the same result as the branded drug.

The DOE was outlined by the Supreme Court in Graver Tank: A patentee’s rights are not limited to the literal wording of claims, but extend to equivalents that a competitor might use to capture the invention’s essence.2 In Graver Tank, the accused infringer substituted one ingredient in its welding composition to avoid the “alkaline earth metal” specified in the claims.3 The two welding compositions, however, were “identical in operation and produce[d] the same kind and quality of weld.”4 The substituted ingredient performed substantially the same function in substantially the same way to achieve the same result as the ingredient in the claimed product. The Supreme Court ruled that the substitution was an insubstantial change, and thus the accused product infringed under the so-called triple identity test of the DOE.5

Two DOE tests

Two tests for the DOE exist: the ”function-way-result” (FWR) test of Graver Tank (also known as the “function-way-result” test) and the insubstantial differences test of Warner-Jenkinson v. Hilton Davis.6 The Supreme Court has approved using either test, as the latter may be “more suitable to different cases, depending on their particular facts.”7 Warner-Jenkinson left room for lower courts, especially the Federal Circuit, to refine how to apply the DOE on a case-by-case basis.8

In sum, the FWR test of Graver Tank holds that “if two devices do the same work in substantially the same way, and accomplish substantially the same result, they are the same, even though they differ in name, form or shape.”9 The insubstantial differences test of Warner-Jenkinson asks whether the differences between the claimed element and the accused element are insubstantial to a person of ordinary skill.10

Application of DOE in pharmaceutical actions generally

In pharmaceutical cases, courts have applied both tests. For example, in Intendis GmbH v. Glenmark Pharmaceuticals Inc., USA, while the function of an ingredient in a dermatological cream was not explicitly stated in the patent claim, the court still applied the triple identity test.11 The court considered the generic’s Abbreviated New Drug Application statements to establish that the substituted ingredient served substantially the same function as the one claimed in the patent.12

Significantly, the Federal Circuit in Mylan Institutional LLC v. Aurobindo Pharma Ltd. suggested that, on remand, the district court should “consider whether the substantiality of the differences test may be more applicable” because “the substantial differences test may be more suitable than FWR for determining equivalence in the chemical arts.”13

In practice, both tests are often used in tandem. The patentee may attempt to show function, way, and result alignment as evidence that any differences are insubstantial. The accused infringer will highlight any differences in either function, way, or result to show the change is not significant.

In Eli Lilly & Co. v. Hospira, Inc., the patent claimed a method of administering pemetrexed disodium in combination with vitamins (folic acid and B12) to reduce toxic side effects.14 Two generics sought Food and Drug Administration approval and deliberately used a salt other than the claimed disodium.15 The Federal Circuit ruled that the generics infringed because the different salt did not significantly change the structure or function of the pemetrexed anion, and that once dissolved in solution for infusion, both salts dissociate completely, releasing the same pemetrexed anion into the bloodstream.16 In other words, the substitution of tromethamine for sodium was deemed an insubstantial difference in the context of the treatment method.

Defenses and limitations to the DOE

Prosecution history estoppel

There are numerous defenses and/or limitations to the use of the DOE, most significantly, prosecution history estoppel (often “file wrapper estoppel”). If a patentee amended a claim or made arguments to the patent examiner, the patentee cannot later claim that the territory surrendered is an “equivalent” and attempt to recapture it.17

Prosecution history estoppel usually arises from amendments to the claims. This is called amendment-based estoppel.18 But not all amendments negate application of the DOE. Rather, under Festo, courts apply a three-part analysis to determine if an amendment bars DOE for a given claim: (1) Was the claim amended to narrow its scope; (2) was the amendment made for a reason related to patentability or was it tangential; and (3) is the accused equivalent within the scope of what was surrendered by the amendment.19

Another form of prosecution history estoppel is argument-based estoppel. If a patentee clearly and unmistakably represents to the U.S. Patent and Trademark Office that the claims do not cover a certain feature or range, the patentee may be estopped from asserting what was disclaimed as an equivalent. But courts require the disclaimer to be clear, although ambiguous prosecution arguments are usually construed against the patentee for public notice reasons.20

Ensnarement

Some courts have added an additional limitation on applying the DOE, i.e., “ensnarement.”21 The ensnarement defense originated in Wilson Sporting Goods Co. v. David Geoffrey & Assocs.22 It requires the patentee to propose a hypothetical claim covering the accused product/process and then establish that the proposed claim would have been allowed by the PTO. The issue is a matter of law for the court, not a jury question, and is often determined in a supplement proceeding.23 Thus, this defense, although not often applied, should be considered by patentees in preparing to asserting infringement under the DOE.

Estoppel from non-U.S. prosecutions

Lastly, statements made in prosecuting foreign counterpart applications are also relevant in applying the DOE.24 In Tanabe Seiyako Co. v. U.S. ITC, the Federal Circuit, in rejecting infringement under the DOE, stated that “the representations made to foreign patent offices are relevant to determine whether a person skilled in the art would consider butanone or other ketones to be interchangeable with acetone in [the patentee’s] claim[s]. … [S]tatements to foreign patent offices suggest to a person skilled in the art that [the solvents in the accused process] may not be interchangeable with the claimed solvents.”25

Survey of recent decisions

The function-way-result/insubstantial difference test

In Galderma Labs., L.P. v. Amneal Pharmaceuticals LLC, the Chang and Ashley II patents claimed topical doxycycline formulations for treating skin conditions.26 In particular, the Chang patents claimed a composition with both an immediate-release and a delayed-release component in a single unit for once-daily dosing.27 Galderma alleged infringement under the DOE, arguing that Amneal’s product contained the equivalent of the claimed 10 mg delayed-release portion. In inter partes review, the Patent Trial and Appeal Board rejected Galderma’s narrow construction of “delayed release” (requiring no substantial release in the stomach) and adopted a broader reading, finding that the claims were not limited to enteric-coated pellets or stomach-bypassing formulations.28 The district court applied this broader definition during litigation and, applying the FWR test, found infringement of the Chang patents. On appeal, the Federal Circuit affirmed infringement for the Chang patents but reversed as to the Ashley II patents.29 Regarding the Chang patents, Amneal argued that argument-based estoppel applied because of statements the plaintiffs made to the Board during inter partes review.30 The court rejected this, explaining there was no disclaimer since the Board expressly rejected the plaintiffs’ narrow interpretation.31 For the Ashley II patents, Galderma’s DOE claim failed for lack of proof. The Federal Circuit emphasized that proving equivalence requires “particularized testimony” and a “linking argument” demonstrating why differences between the accused product and the claimed invention are insubstantial.32 Because Galderma did not present the necessary testimony, there was no infringement of the Ashley II patents.

In Amgen Inc. v. Sandoz Inc., the patents claimed a method of purifying protein formulations.33 Amgen alleged infringement under the DOE, relying on the insubstantial differences test to show that Sandoz’s process was equivalent to the claimed invention. Amgen argued that because Sandoz’s purification method involved steps serving the same function as the patented “washing and eluting” steps, it operated in substantially the same way.34 At the district court, Amgen’s case faltered because the court applied the FWR test and found that Sandoz’s process did not adequately meet the “way” criteria.35 That is, it did not perform the claimed step in the same way as Amgen’s three-step “refolding,” “washing,” and “eluting” sequence.36 On appeal, the Federal Circuit affirmed. The appellate court further warned that accepting Amgen’s argument would improperly extend the claims to cover “nearly any type of adsorbent chromatographic separation,” thereby expanding the claim beyond what was actually patented.37

In Mylan Institutional LLC v. Aurobindo Pharma Ltd., the dispute arose over patents covering a dye used to map a patient’s lymph nodes.38 The District Court for the Eastern District of Texas granted Mylan a preliminary injunction after finding infringement under the DOE.39 The court’s equivalence analysis relied on the FWR test, but failed to conduct the required limitation-by-limitation comparison between the claimed invention and Aurobindo’s accused process.40 On appeal, the Federal Circuit held that the district court’s analysis was legally flawed because it treated the “function” and “way” prongs as one. This resulted in the “way” analysis being not adequately addressed.41 Aurobindo argued that their two reagents oxidized in different ways from the original patent, providing sufficient doubt to defeat the preliminary injunction with regards to the process patents. The appellate court also questioned whether the insubstantial differences test, rather than the FWR test, might have been more appropriate for this technology.42

Dedication-disclosure doctrine

In Eagle Pharmaceuticals Inc. v. Slayback Pharma LLC, the patent claimed a ready-to-use liquid formulation of a chemotherapy drug that included a specific solvent.43 Slayback’s accused product used ethanol, a solvent explicitly disclosed in the patent’s specification as a possible alternative to the claimed solvent.44 During litigation, Eagle argued that Slayback’s use of ethanol was equivalent under the DOE. The Federal Circuit disagreed, applying the dedication-disclosure doctrine. Because the alternative solvent was disclosed in the patent’s specification but left unclaimed, it was deemed dedicated to the public.45 As a result, Eagle could not rely on the DOE to cover Slayback’s formulation.

In Indivior Inc. v. Dr. Reddy’s Labs., S.A., the patent claimed drug-delivery films containing specific polymers that formed the structure of the dissolvable strips.46 Dr. Reddy’s product used a different polymer than what was claimed in the original patent. However, this polymer was disclosed in Indivior’s patent specification as a possible option for making the film.47 Consequently, Indivior could not use the DOE to assert that Dr. Reddy’s formulation infringed.

Prosecution history estoppel

In Pharma Tech Solutions, Inc. v. LifeScan, Inc., the patent covered technology for measuring blood glucose concentrations.48 The device used an electrochemical sensor that takes multiple current readings, converts those readings into analyte concentrations, and then compares the concentrations to one another in a linear fashion.49 As Lifescan’s infringed product did not literally match the claim language, Pharma Tech relied on the DOE. During patent prosecution, the patentee amended their claims to add the “conversion” and “comparison” steps, thus narrowing the scope to overcome prior art.50 The Federal Circuit held that these amendments, made for reasons related to patentability, triggered the presumption of prosecution history estoppel under Festo.51 The court further found that the patentee had also made prosecution statements emphasizing the importance of the conversion and comparison steps, which independently supported argument-based estoppel.52 Because Pharma Tech could not rebut the presumption or fit within a recognized exception in Festo, the court concluded that the claims could not, under the DOE, cover LifeScan’s device.

In Amgen Inc. v. Amneal Pharmaceuticals LLC, the patent claimed a pharmaceutical composition used to treat hyperparathyroidism and hypercalcemia.53 “Binder starch” was a key component of the claimed formulation.54 Amneal’s product used a different binder, so there was no literal infringement. Therefore, Amgen used the DOE to argue infringement. During patent prosecution, Amgen amended the claims to specifically require binder starch, narrowing the scope to overcome prior art.55 On appeal, Amgen argued that the amendment was made for reasons unrelated to patentability and therefore should not trigger prosecution history estoppel.56 The Federal Circuit rejected this argument, holding that Amgen failed to prove the amendment fell outside the Festo presumption.57 Because the narrowing of claims was for patentability and no exception applied, the court concluded that Amgen could not use the DOE to capture Amneal’s product that employed a different binder.

In Amgen Inc. v. Coherus BioSciences, Inc., the patent claimed a method of purifying proteins that included specific combinations of salts.58 During patent prosecution, the examiner rejected Amgen’s claims as obvious over the Holtz reference, which disclosed several salts for improving interactions between a protein and a chromatography column.59 In response, Amgen argued that Holtz did not teach (1) a combination of salts, (2) combining the particular salts recited in the claims, or (3) using salts to improve the dynamic capacity of the column.60 The claims were amended to recite the specific combinations, and this specification emphasized that the invention covered only these “particular” salt combinations.61 The Federal Circuit held that this language, combined with the amendment made for patentability reasons, triggered prosecution history estoppel under Festo.62 Because Amgen could not rebut the presumption, the court concluded that the DOE could not extend the claims to cover Coherus’ different salt combination.

In Colibri Heart Valve LLC v. Medtronic CoreValve, LLC, the patent claimed a method for implanting an artificial heart valve that allows for repositioning if placement was initially incorrect.63 To overcome a written description rejection during prosecution, Colibri canceled a second independent claim that covered the retraction of the moveable sheath to expose part of the heart valve device.64 Instead, the amended claim recited “pushing out the pusher member.”65 At trial, Colibri argued that Medtronic’s artificial heart valve, which was operated by retracting the sheath, was equivalent under the DOE. The District Court for the Central District of California ruled in Colibri’s favor, finding infringement and awarding more than $100 million in damages.66 Colibri argued that because it had not amended any claims to exclude a method involving the retraction of a moveable sheath, but had merely canceled it as a separate independent claim, prosecution history estoppel did not apply and equivalence could be found.67 The Federal Circuit reversed this ruling and held that the cancellation of the retraction claim conveyed a clear surrender of that method, triggering prosecution history estoppel.68 This prevented Colibri from using the DOE to allege infringement.

Limiting language

In Enzo Biochem Inc. v. Applera Corp., the patents involved methods for detecting nucleic acids using chemical labeling techniques.69 The specification described two different approaches: a direct detection method, in which the label was directly attached to the probe, and an indirect detection method, which used an intermediate moiety to link a probe to the label.70 While both methods were discussed in the patent, the claims recited only the indirect detection method.71 Enzo accused Applera of infringement under the DOE, asserting that Applera’s direct detection method was equivalent to the claimed indirect method. Enzo argued that despite the structural and procedural differences, the two methods performed the same function, in the same way, to achieve the same result, and thus should be considered interchangeable for infringement purposes.72 The Federal Circuit rejected this argument. Even though the claims did not explicitly exclude direct detection, the court interpreted the patent’s language as confining the invention to the indirect method.73 Because the patent itself framed the invention in this narrower way, Enzo could not rely on the DOE to reach the unclaimed direct detection approach.

Finding infringement under the DOE

In Bio-Rad Labs., Inc. v. 10X Genomics Inc., the patents at issue related to micro-fluid systems that used fluorinated microchannels for biological analysis.74 Bio-Rad alleged infringement under the DOE. 10X raised two main defenses: prosecution history estoppel and claim vitiation.75 The Federal Circuit affirmed the district court’s rejection of both defenses. Regarding prosecution history estoppel, the court found no clear and unmistakable surrender of relevant subject matter during prosecution.76 Bio-Rad had not narrowed its claims in a way that would bar it from asserting equivalence. On claim vitiation, the court emphasized that the DOE does not fail merely because the accused product or method differs from the literal claim language.77 The test is whether the difference is substantial. Bio-Rad provided proof that the accused microchannels performed the same function in substantially the same way, to achieve the same result as the Bio-Rad’s claimed method.78 Therefore, the Federal Circuit upheld the district court’s finding of infringement under the DOE.

In Cadence Pharmaceuticals, Inc. v. Exela PharmSci., Inc., the patents claimed a pharmaceutical process for stabilizing aqueous acetaminophen formulations.79 This method required that oxygen levels be kept below a specified parts-per-million threshold during manufacture.80 Even though Exela’s process did not literally meet the oxygen limit in the claims, the difference was small enough that the process still performed the same function, in the same way, to achieve the same result.81 Exela argued that if Cadence were allowed to treat a process with higher oxygen levels as equivalent to one that met the limit, then the oxygen restriction in the patent would no longer matter.82 This would “vitiate” the claim limitation by effectively eliminating the oxygen-level requirement. The district court rejected this argument, holding that Cadence’s theory preserved the limitation because the accused process still meaningfully satisfied the low-oxygen requirement.83 The appellate court also upheld equivalence based on the testimony of Cadence’s expert, who provided sufficient function-way-result analysis.84 On appeal, the Federal Circuit found no error in the district court’s rejection of vitiation and upheld its finding of infringement under the DOE.

In Verinata Health, Inc. v. Ariosa Diagnostics, Inc., the patents at issue covered methods for prenatal DNA testing technology, specifically analyzing cell-free fetal DNA from maternal blood samples.85 Verinata alleged that Ariosa’s testing method infringed the patents both literally and under the DOE. At the district court, Verinata presented detailed testimony from its expert witness, Dr. Cooper, who walked through the claims element by element and compared each to Ariosa’s accused method under the FWR framework.86 Dr. Cooper testified that the readout cassettes and amplicons served substantially the same function (“immobiliz[ing] onto a solid support”) in substantially the same way, through “hybridization of [the] DNA molecule,” to achieve the same result: “detection of the target sequences that were in the original mixture.”87 The court found literal infringement, but it also ruled that even if literal infringement were absent, equivalence was satisfied because the expert’s testimony alone met the requirement for particularized evidence and a linking argument for each limitation.88 On appeal, the Federal Circuit affirmed that Dr. Cooper’s element-by-element analysis provided sufficient proof to support DOE as an alternative basis for infringement.

In Intendis GmbH v. Glenmark Pharmaceuticals Inc., USA, the patents at issue claimed a topical treatment containing a specific molecular component designed to enhance skin penetration.89 Intendis argued that Glenmark’s formulation, while using a different molecule, performed substantially the same way to achieve the same result.90 The plaintiffs’s expert testified that Glenmark’s use of isopropyl myristate served the same function of enhancing penetration through the skin barrier, operated in the same way by interacting with the stratum corneum to improve permeability, and achieved the same result of increased delivery as did Intendis’s claimed triglyceride and lecithin.91 The district court found that this testimony satisfied the FWR test and established infringement.92 On appeal, the Federal Circuit affirmed, emphasizing that expert testimony can provide sufficient evidence to prove equivalence under the DOE.

Reverse DOE (RDOE)

Under the reverse DOE (RDOE), even if an accused product literally infringes a patent claim, it may nonetheless be deemed non-infringing if it is so far changed in principle that it performs the same or similar function in a substantially different way.93

In practice however, the Federal Circuit has never affirmed a judgement of non-infringement based on the RDOE.94 In the wake of Steuben Foods, the notion that RDOE was dead, or a “doctrinal relic” grew amongst practitioners and commentators. Some argue that the reverse DOE has been ignored by courts, buried by the Patent Act of 1952, and/or subsumed by Section 112.95 Others have claimed that Aro Manufacturing Co. v. Convertible Top Replacement Co. stated that 1952 Act “left intact the entire body of case law on direct infringement.”96

How to effectively use the RDOE

RDOE is an affirmative defense and must be pled under Rule 8(c). Due to the factual nature of the defense, the need for early disclosure of the defense is heightened.97 In Kewazinga Corp. v. Microsoft Corp., the court allowed Microsoft’s reverse DOE defense to proceed to trial.98 It was not successful.

The most reliable way to preserve a successful RDOE defense on appeal is to ensure the jury decides the issue because a jury verdict is reviewed under the “substantial evidence” standard whereas judicial determinations are reviewed de novo. Defendants can look to SRI International v. Matsushita Elec. Corp. of Am. for an example of effective jury instructions.99 Others have followed SRI International’s formulation, such as the jury instructions in Echometer Co. v. Lufkin Industries: “where a device is so far changed in principle from a patented article that it performs the same or similar function in a substantially different way, but nevertheless falls within the literal words of the claim.”100

Lastly, the RDOE provides a unique tool against non-practicing entities. Non-practicing entities are less vulnerable to counterclaims and are more likely to pursue expansive claim interpretation. The RDOE can rebut this and reframe the dispute around how the accused product works.

Avoiding prosecution history estoppel

Before filing

Avoiding prosecution history estoppel begins even before a patent application is drafted by conducting a thorough prior art search. Recognizing the contours of the prior art will allow patent practitioners to draft and file claims that avoid earlier disclosures that will later necessitate amending the as-filed claims. Indeed, this may be the best way to avoid the Festo presumptions arising from claim amendments. Although difficult, draft claims, albeit broad, that are reasonable in scope considering the prior art.

Ensure that the disclosure in the specification is consistent with the scope of the claims. That is, to avoid the disclosure-dedication problem, ensure that the specification has not disclosed more options or possibilities for the invention than are covered by the claims. A disclosure-dedication defense to DOE becomes more complicated when original claims are amended. If the claims are amended to exclude certain aspects of the invention disclosed in the specification, reliance on DOE may be excluded.

Before amending

When possible, before amending any claim, argue that the rejection is improper. The simplest example is that a cited reference is not prior art. Also consider that certain claim limitations are missing in the prior art or that there is no teaching to combine the cited references under Section 103. Indeed, an interview with the examiner could assist in removing or recasting the rejection to avoid amending the claims. At a minimum, the number of rejections may be limited and thus limit the scope of any amendment. If an amendment is required, limit its scope to the extent possible. For example, add only one limitation; others, if needed, can be added later.

When amending

To the extent possible, attempt to explain the reason for the amendment, i.e, it does not relate to patentability, but the amendment is only tangential under Festo. In judging tangentiality, courts will not consider extrinsic evidence. Reasons for the amendment must therefore be supplied in the prosecution history.

In amending any claim, consider its effect on the DOE. Consider what is being surrendered and how that may limit applicability of the DOE. In this regard, input from the inventor(s) could be particularly useful in explaining possible equivalents.

Avoid criticizing a feature in the prior art to distinguish the invention. If this is ignored, that feature may be excluded from coverage under the DOE.

Understand that amendments or statements in one prosecution can affect coverage of related patents. Thus, consider the portfolio as a whole when prosecuting related applications.

One might assume that cancelling a rejected claim rather than amending it will avoid the Festo presumptions. However, cancelling claims, even independent claims, can limit reliance on the DOE for non-amended claims. One must consider how the scope of the cancelled claims affects the scope of other pending claims.

Lastly, with or without an amendment, statements made in prosecution can create an estoppel. Although difficult, consider all statements for their possible effect on the DOE. Tailor statements to the precise rejection rather than expanding on other aspects of the invention.

The authors wish to thank Mia Pakola, legal intern, for her assistance with this article.

  1. Cornell Law School, Doctrine of Equivalents, Legal Information Institute, https://www.law.cornell.edu/wex/doctrine_of_equivalents (last visited September 10, 2025).

  2. Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605 (1950).

  3. Id. at 610.

  4. Id.

  5. Id. at 608–12.

  6. Warner-Jenkinson Co., Inc. v. Hilton Davis Chem. Co., 520 U.S. 17 (1997).

  7. Id. at 39–40.

  8. Id. at 40.

  9. 339 U.S. at 608 (internal quotation marks omitted).

  10. 520 U.S. at 39–40.

  11. 822 F.3d 1355, 1361–63 (Fed. Cir. 2016).

  12. Id.

  13. 857 F.3d 858, 869 (Fed. Cir. 2017) (citing 520 U.S. at 40).

  14. 933 F.3d 1320, 1325–26 (Fed. Cir. 2019).

  15. Id. at 1326, 1328.

  16. Id. at 1335–36.

  17. See Hoganas AB v. Dresser Indus., Inc., 9 F.3d 948, 950 n.6 (Fed. Cir. 1993).

  18. See Hilgraeve Corp. v. McAfee Assocs. Inc., 224 F.3d 1349, 1355 (Fed. Cir. 2000); Hughes Aircraft Co. v. U.S., 717 F.2d 1351, 1362 (Fed. Cir. 1993).

  19. See Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., 535 U.S. 722, 740–741 (2002); see also Brian Coggio & James Huguenin-Love, Potential Ways for Avoiding the Presumption of Prosecution History Estoppel of an Allowable Dependent Claim Depending from a Rejected Independent Claim, Fish Blog (April 28, 2020), https://www.fr.com/insights/thought-leadership/blogs/potential-ways-for-avoiding-the-presumption-of-prosecution-history-estoppel/.

  20. See Cordis Corp. v. Medtronic Ave, Inc., 511 F.3d 1157, 1177 (Fed. Cir. 2008); see also Anderson Corp. v. Fiber Composites, LLC, 474 F.3d 1361, 1374 (Fed. Cir. 2007).

  21. For a full discussion of ensnarement, see Brian Coggio & Ron Vogel, “The Doctrine of Equivalents and Its Limitations, Including ‘Ensnarement,’ a Particularly Potent Defense,” 25 IP Litigator, 1 (September/October 2019).

  22. 904 F.2d 677 (Fed. Cir. 1990).

  23. Depuy Spine, Inc. v. Medtronic Sofamor Danek, Inc., 515 F. Supp. 2d 206, 208 (D. Mass. 2007); see also Jang v. Boston Sci. Corp., 872 F.3d 1275, 1288 (Fed. Cir. 2017).

  24. See Caterpillar Tractor Co. v. Berco, S.P.A., 714 F.2d 1110, 1116 (Fed. Cir. 1983).

  25. 109 F.3d 726, 733 (Fed. Cir. 1997).

  26. 806 Fed. Appx. 1007, 1008 (Fed. Cir. 2020).

  27. Id. at 1008–09.

  28. Id. at 1009–11.

  29. Id. at 1008.

  30. Id. at 1010.

  31. Id. at 1011.

  32. Id. at 1013–14.

  33. 923 F.3d 1023, 1026 (Fed. Cir. 2019).

  34. Id. at 1028–29.

  35. Id. at 1029.

  36. Id.

  37. Id.

  38. 857 F.3d at 861.

  39. Id.

  40. Id. at 867.

  41. Id. at 868–69.

  42. Id.

  43. 958 F.3d 1171, 1173 (Fed. Cir. 2020).

  44. Id. at 1174.

  45. Id. at 1176–77.

  46. 930 F.3d 1325, 1331 (Fed. Cir. 2019).

  47. Id. at 1346–47.

  48. 942 F.3d 1372, 1374 (Fed. Cir. 2019).

  49. Id. at 1375.

  50. Id. at 1379.

  51. Id. at 1379.

  52. Id.

  53. 945 F.3d 1368, 1371 (Fed. Cir. 2020).

  54. Id. at 1373.

  55. Id.

  56. Id. at 1381–82.

  57. Id.

  58. 931 F.3d at 1156.

  59. Id. at 1157.

  60. Id. at 1160.

  61. Id.

  62. Id. at 1160–61.

  63. 143 F.4th 1367, 1369 (Fed. Cir. 2025).

  64. Id. at 1369–70, 1379.

  65. Id. at 1372.

  66. Id. at 1370.

  67. Id. at 1379–81.

  68. Id.

  69. 702 Fed. Appx. 971, 972 (Fed. Cir. 2017).

  70. Id. at 972–73.

  71. Id. at 974.

  72. Id. at 975–76.

  73. Id. at 976–77.

  74. 967 F.3d 1353, 1360 (Fed. Cir. 2020).

  75. Id. at 1363.

  76. Id. at 1365–66.

  77. Id. at 1367–68.

  78. Id. at 1368.

  79. 780 F.3d 1364, 1367 (Fed. Cir. 2015).

  80. Id.

  81. Id. at 1370–71.

  82. Id. at 1371.

  83. Id. at 1371–72.

  84. Id. at 1370.

  85. 809 Fed. Appx. 965, 967 (Fed. Cir. 2020).

  86. Id. at 972–73.

  87. Id. at 973.

  88. Id.

  89. 822 F.3d at 1358.

  90. Id. at 1360.

  91. Id. at 1361.

  92. Id. at 1361–62.

  93. Boyden Power-Brake Co. v. Westinghouse, 170 U.S. 537, 568 (1898).

  94. Steuben Foods, Inc. v. Shibuya Hoppmann Corp., 127 F.4th 348, 357 (Fed. Cir. 2025) (“We have never ‘affirmed a decision finding noninfringement based on the reverse doctrine of equivalents.’”) (quoting Tate Access Floors, Inc. v. Interface Architectural Res., Inc., 279 F.3d 1357, 1368 (Fed. Cir. 2002)).

  95. Id.

  96. Aro Mfg. Co. v. Convertible Top Replacement Co., 377 U.S. 476, 483 (1964).

  97. Roche Palo Alto LLC v. Apotex, Inc., 531 F.3d 1372, 1377 (Fed. Cir. 2008).

  98. 558 F. Supp. 3d 90, 112–13 (S.D.N.Y. 2021).

  99. 775 F.2d 1107 (Fed. Cir. 1985).

  100. Echometer Co. v. Lufkin Indus., Inc., No. 7:00-CV-101-R, 2003 WL 21768011 (N.D. Tex. July 31, 2003); 775 F.2d at 1123.

The opinions expressed are those of the authors on the date noted above and do not necessarily reflect the views of Fish & Richardson P.C., any other of its lawyers, its clients, or any of its or their respective affiliates. This post is for general information purposes only and is not intended to be and should not be taken as legal advice. No attorney-client relationship is formed.