Guest Column | October 23, 2018

A Biosimilar Manufacturer's Sword & Shield Against Doctrine Of Equivalents Claims

By Nicolas Arkells, CEO, Manticore Consulting Group


While biosimilar manufacturers face many unique challenges in patent litigation, one of the most common is an infringement action brought under the doctrine of equivalents (DOE). DOE is a principle where a party sues for infringing on the general spirit of the patent, rather than on the specific content of its claims. The criteria for DOE centers around whether the infringer’s product performs substantially the same thing in a similar manner. (For more on DOE, read my previous article.)

Fortunately, a biosimilar defending against a patent infringement claim based on DOE may have both an offensive and a defensive option known as prosecution history estoppel (PHE). In this term, “prosecution” refers to the patent application process rather than its more common definition. “History” refers to the documentation compiled as part of the patent application and that the timeline looks backward from the approval date. “Estoppel” is a legal term used to convey “detrimental reliance.”

Although PHE can be complicated, at its core, this doctrine is intended to keep a patent holder from abusing DOE to capture content beyond the original claims. For example, if the patent holder of a biologic had to make their claims more specific to obtain approval from the U.S. Patent and Trademark Office (USPTO), those amendments could be used against them in a patent infringement suit if they bring legal action against a biosimilar manufacturer under DOE. The overall purpose of PHE is to provide the courts with a way to keep DOE from being used to retroactively claim things beyond the original scope of the patent. A successful PHE counterattack to a DOE claim results in shifting the burden to the patent holder, requiring them to prove the amendment was unrelated to obtaining patentability. If the patent holder is unsuccessful at disproving PHE, they will not be able to use DOE to broaden the scope of their claims; instead they will have to rely on the narrower interpretation originally submitted to the USPTO. This makes it very difficult to successfully bring a patent infringement claim against a biosimilar manufacturer since the only alternative to DOE is literal infringement, which is very difficult is to prove.

However, PHE can be defeated if the patent holder can successfully argue the equivalent was unforeseeable at the time of the application (something originator biologic manufacturers aren’t likely to successfully claim when challenging a biosimilar). Another way to overcome PHE is if the amendment was only tangentially related to the claim, for example, when a claim is amended for greater clarity. The final way would be if the court found exceptional circumstances it felt would not warrant enforcing PHE; unfortunately, the Supreme Court has given little guidance as to what circumstances might warrant this determination.

Origins & Policy of Prosecution History Estoppel
The primary case setting forth the guidelines for PHE is the Supreme Court holding from Festo Corp. v. Shoketsu.1 When DOE is raised, if an alleged infringer can counter with a valid PHE defense, the patent holder will generally have the burden of disproving the presumption their DOE claim is invalid. However, Festo Corp. v. Shoketsu gave the patent holder two ways to counter PHE.1 A patent holder could defeat PHE claims by either claiming the amendment was so minor it was insignificant or that the equivalent was unforeseeable at the time the claims were written.1 The second option addressing foreseeability of later innovations is basically to protect pioneer technologies which are often so new sometimes their full use is not entirely understood at the time of filing. This is important because it is a policy protection biologic sponsors could try to obtain, as the consideration of being a “pioneer technology” is assessed at the time of filing the patent, not the current dispute. Often the case law surrounding PHE as applied to biosimilars is derived from generic drug manufacturer disputes, as it is far more evolved than the case law specifically related to biosimilars. Further, regardless of the ongoing debate about how parallel biosimilars are or aren’t to generics, the courts generally find them to be one and the same, especially from a policy perspective.

Application to Biologics/Biosimilars
The case UCB, Inc. v. Yeda Research & Dev. Co. addresses PHE directly, as it pertains to biologic humanized monoclonal antibodies.2 In this case, the patent holder had narrowed their claims to achieve patentability during the application process, specifically to distinguish them from prior art.2 Distinguishing a claim from prior art is a requirement of the USPTO for patentability in which an applicant must ensure their idea is not too much like what has already been discovered. Narrowing a claim is the actual process where the party filing a patent is told to make its claims more specific or it won’t receive approval from the USPTO. Because of an amendment to its application, the patent holder could not claim DOE on anything addressed in the original form, only the amended one.2 In this situation, it meant the patent holder was unable to support an infringement action against the humanized antibody, which essentially performed the same thing as their antibody but applied to people instead of mice.2 The court felt this was not infringement under DOE because the claims had been narrowed to avoid this for the original patent to be approved, thus surrendering a broader application.2 PHE allowed the alleged infringer in this case to use the patent holder’s own claim application against them as an offensive weapon.

Some courts are stricter than in UCB, though. For example, in Intendis GmbH v. Glenmark Pharm. Ltd., when dealing with a dispute between a generic drug producer and a patent holder of the original drug, the court focused on a technicality.3 When DOE was asserted, the generic owner argued it was barred by PHE.3 The court felt that although the claim was amended to narrow its scope, it was not narrowing so much as it was “clarifying,” and, thus, it was not sufficiently related to patentability.3 It is worth noting this case is somewhat of an anomaly.

Recent Success of PHE in Generic Drug Manufacturer Disputes
In a court of appeals case, Spectrum Pharm., Inc. v. Sandoz Inc., a generic drugmaker used PHE very successfully, not only as a shield, but also as a sword.4 When the generic producer received approval of its abbreviated new drug application (ANDA), the patent holder sought to sue for infringement under DOE.4 The court found that when the inventor surrendered the claim regarding lower quantities of dosage to comply with the USPTO’s concerns over obviousness, it had surrendered any use of DOE on those claims as well.4 But the court then took it a step further, finding the claims of the patent holder for the application of treatment using the drug were invalid for being obvious.4 The generic manufacturer not only defeated the DOE claim, but then used PHE as a sword to destroy several of the patent claims regarding its therapeutic application. This is critical because a court holding that finds a claim is obvious not only defeats the infringement claim at trial, it also causes considerable economic damage for the patent holder, as they can no longer enforce those claims against any current or future parties.

Other Potential Considerations
Although Intendis GmbH was more of an outlier, it is still a cautionary tale though of what could happen as lower courts struggle with the more abstract concepts of patent law such as PHE. In Abbott Labs. v. Dey, L.P., the court held even if a claim has not been amended for patentability, a PHE claim can be raised based on statements related to those claims during patent filing.5 Therefore, depending on the court, it may be possible to use testimony or emails in addition to the prosecution history itself, which is critical as the USPTO archives its emails with the intent they will be available for use in litigation. The court was careful to limit this holding to only the patent in question; the alleged infringer couldn’t use previous similar prior patent filing statements, even if they were filed by the same inventor for similar subject matter.5

Part of the reason for these high levels of variability involving DOE and PHE disputes is the amount discretion courts may exercise. This is because they are both viewed as a matter of law (subject to the judge’s discretion), not fact (usually juries are the fact finder). However, this can be beneficial because if a party doesn’t achieve the results they had hoped for at trial, findings of law can be the sole grounds for an appeal. Further, the criteria for presenting these challenges is much lower than asking a court of appeals to overturn a finder of fact. DOE & PHE disputes are reviewed in the appeals process as “de novo” (as new), allowing less constraint when challenging a holding surrounding those issues, as parties are not as bound by a lower court’s holding on appeal.

Although PHE can be enigmatic and technical, it is a critical tactic for biosimilar manufacturers to use if they plan on marketing their product while there are still active patents on related biologics. This is because PHE allows the biosimilar manufacturer to limit the scope of DOE claims brought against them by the original biologics manufacturer. Biosimilars also have the advantage of being able to draw from favorable case law surrounding generic drugs, as courts tend to find a great deal of similarity between generic small molecule drugs and biosimilars. Another advantage for biosimilars is that public policy favors them, as they are seen by many courts as a fundamental tool to reduce healthcare costs.  


  1. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 122 (S. Ct. 1831, 152 L. Ed. 2d 944 [2002]).
  2. UCB, Inc. v. Yeda Research & Dev. Co., 117 F. Supp. 3d 755 (E.D. Va. 2015), appeal dismissed (Aug. 25, 2015), aff'd, 837 F.3d 1256 (Fed. Cir. 2016).
  3. Intendis GMBH v. Glenmark Pharm. Ltd., 117 F. Supp. 3d 549, 580 (D. Del. 2015), aff'd sub nom. Intendis GMBH v. Glenmark Pharm. Inc., USA, 822 F.3d 1355 (Fed. Cir. 2016).
  4. Spectrum Pharm., Inc. v. Sandoz Inc., 802 F.3d 1326 (Fed. Cir. 2015).
  5. Abbott Labs. v. Dey, L.P., 287 F.3d 1097 (Fed. Cir. 2002).
  6. Arkells N, Chopra A, Chopra I. Biosimilar Regulatory Policies Issues and Implications: Where Are We Headed? 23rd Annual International Meeting of the International Society for Pharmacoeconomics and Outcomes Research, Baltimore, MD, United States, 2018.

About The Author :
Nicolas Arkells is the CEO at Manticore Consulting Group, a global health economics and outcomes consulting firm. He has over 15 years of leadership experience ensuring organizational commitment to statistical analysis and implementation. His law and science juris doctorate concentrated on intellectual property, which encouraged his research in biotechnology, market access, policy, and patent law. His MBA focused on the application of analytics to provide solutions to real-world problems in the healthcare industry. He is certified in medical devices and pharmaceuticals by the Regulatory Affairs Professionals Society, Lean Six Sigma black belt-trained in the healthcare industry, agile-certified as a PSM and PSPO, and certified in global human capital through Columbia University. He has been recognized for excellence in legal research, leadership, and alternative dispute resolution and as a U.S. biosimilar policy expert. You can reach him via email or connect with him on LinkedIn