IPR or EPR? Five Scenarios and a Decision Tree for Post-Grant Patent Challengers in the Life Sciences

The total number of petitions for inter partes review (IPR) at the Patent Trial and Appeal Board (PTAB) has plummeted over the last year, corresponding closely with the USPTO Director’s 2025 changes to the discretionary denial framework for AIA Trial institution decisions.[1]

This trend is also evident in IPR petitions challenging patents in Technology Center 1600 (biotechnology and organic chemistry)—the primary technology center for biotech and pharma patents.

While the number of biotech and pharma AIA petitions represents a fraction of the total number of petitions at the PTAB, the decline in IPR petitions filed in TC1600 is unmistakable, plunging to an average of only five IPR petitions per quarter over the last nine months. The total number of PGR petitions in TC1600 during this same timeframe has remained relatively low, averaging around five PGR petitions per quarter.

As the number of IPR petitions has declined, the number of requests for ex parte reexamination (EPR) has steadily increased, indicating that patent challengers may be shifting venue preferences.

Examining the EPR data in TC1600 shows a similar increase, although the sample size of EPRs in TC1600 is much smaller, with less than 10 requests per quarter.

As widely discussed in other outlets, this shift in filing dynamics is likely due to the fact that EPRs are not subject to all of the same discretionary denial hurdles that AIA petitioners currently face at the PTAB. See e.g., Magnolia Medical Technologies, Inc. v. Kurin, Inc.[2] Indeed, AIA petitioners must grapple with discretionary denial issues such as parallel litigation (see e.g., Apple Inc. v. Fintiv, Inc.[3]), serial petitions (see e.g., General Plastic Industrial Co., Ltd. v. Canon Kanushiki Kaisha[4]), alternate claim constructions between forums (see e.g., Revvo Technologies, Inc. v. Cerebrum Sensor Technologies, Inc.[5]), settled expectations (see e.g., Dabico Airport Solutions Inc. v. AXA Power APS[6]; Home Depot USA, Inc. v. H2 Intellect LLC[7]), and foreign sovereignty (see e.g., Tianma Microelectronics Co., Ltd. v. LG Display Co., Ltd.[8])—all prior to IPR or PGR trial institution. To date, these same issues have had minimal impact, if any, when requesting EPR. Additionally, the substantial new question (SNQ) of patentability threshold for granting EPR is lower than the “reasonable likelihood” and “more likely than not” thresholds for instituting IPR and PGR, respectively. See 35 U.S.C. §§ 314(a) and 324(a). Indeed, historically, EPRs have an institution rate near 90%. The current institution rate for IPRs is less than 40%.

EPRs can also be advantageous in that they are not subject to same 35 U.S.C. §§ 315(e)(2) and 325(e)(2) litigation estoppels like IPRs and PGRs. Under these provisions, a petitioner (or its RPI or privy) from an IPR or PGR that reaches a Final Written Decision is estopped from asserting in a civil action or ITC proceeding invalidity arguments that the petitioner raised or reasonably could have raised during the IPR or PGR. No such estoppel applies to a requestor from a completed EPR, meaning a patent challenger can still raise invalidity arguments in litigation that were raised or reasonably could have been raised in the EPR.

But EPRs have their limits, too. Most notable is the patent challenger’s inability to participate in the reexamination once it is ordered. There are no depositions, responsive briefing, or oral arguments for the requestor. All they can do is watch from the sidelines. Moreover, patent owners often successfully amend and add claims in EPRs, emerging from the proceeding with more and/or stronger claims. And historically only about 15-20% of EPRs result in a cancellation of all claims.[9] The ease of amending claims in EPRs may also make the proceeding less attractive for challengers if the patent owner can emerge from the EPR with new claims that specifically cover the challenger’s product, which may have been a design-around, and overcome any asserted prior art. And while EPRs are not subject to the litigation estoppels of §§ 315(e)(2) and 325(e)(2), the estoppel provisions of §§ 315(e)(1) and 325(e)(1) do apply. Sections 315(e)(1) and 325(e)(1) prevent a petitioner (or its RPI or privy) from an IPR or PGR that reaches a Final Written Decision from requesting or maintaining a proceeding “before the Office” based on any ground that the petitioner raised or reasonably could have raised during the IPR or PGR. Thus, if AIA petitioners intend to seek EPR as a backup plan, they should file the request for EPR well before the PTAB reaches its Final Written Decision in the AIA trial.[10]

Given the changes at the PTAB regarding AIA trial discretionary denials, one might speculate that biotech and pharma patent challengers are choosing EPRs after unsuccessful attempts at IPR or PGR. But this has rarely been the case. In examining TC1600 EPRs filed in 2025-2026, we found that 53% of the challenged patents (16 of 30 EPRs) were associated with active, co-pending litigation. But only 3% (1 of 30) were associated with a prior AIA challenge. This suggests that over the last year, EPRs are primarily being used as a litigation-adjacent tool (or independent of litigation altogether), rather than a follow-on to failed AIA challenges.

So, if not for a previously failed AIA challenge, why would a patent challenger choose to file an EPR? Below are five scenarios.

1. AIA Challenge Is Precluded By Statutory Bar

Perhaps the most straightforward reason a patent challenger might choose EPR over AIA challenge is when the challenger is statutorily barred from AIA challenge.

For example, 35 U.S.C. § 315(b) precludes a patent challenger from filing an IPR petition “more than 1 year after the date on which the petitioner, real party in interest, or privy of the petitioner is served with a complaint alleging infringement of the patent.” There are no statutory time bars on EPRs tied to litigation. The § 315(b) time bar may have played a role in Natera, Inc. v. CareDx, Inc., 1-20-cv-00038 (D. Del.). There, Natera served a complaint of patent infringement on CareDx in March 2020, alleging infringement of U.S. Patent No. 10,597,724, which relates to analyzing genetic data from cell-free DNA samples.

In December 2023, the court granted CareDx’s motion for summary judgment that claims of the ’724 patent were invalid under 35 U.S.C. § 101. Natera appealed to the Federal Circuit. In June 2025, while Natera’s Federal Circuit appeal was still pending, an anonymous party filed a request for EPR of the ’724 patent—EPR no. 90/019,992. Did CareDx file a request for EPR as a fallback option if the Federal Circuit were to reverse the district court’s summary judgment on invalidity?

Other IPR petitioners may find themselves barred under 35 U.S.C. § 315(a) (or § 325(a) for PGRs), which precludes filing an AIA petition if the petitioner (or a real party in interest) previously filed “a civil action challenging the validity of a claim of the patent.” Section 315(a) may have played a role in Tiger Biosciences v. MiMedx Group, Inc., 7-25-cv-00161 (W.D. Tex). In April 2025, Tiger Biosciences filed a declaratory judgment action for invalidity (and noninfringement) of U.S. Patent No. 8,642,092, which relates to placental tissue grafts. In March 2026, an anonymous party requested EPR of MiMedx’s ‘092 patent—EPR no. 90/016,024. With no option for IPR due to § 315(a), did Tiger Bioscience opt to file an EPR against the ’092 patent?

2. EPR Challenges Can Avoid AIA Discretionary Denial Pitfalls

As noted above, AIA petitioners may face discretionary denial issues that do not impact requests for EPRs.

Serial patent challenges:

Serial patent challenges in AIA proceedings will face strict scrutiny under Board precedent such as General Plastic.[11] Serial EPR challenges, however, are fair game.

• In Enzo Life Sciences Inc. v. Becton Dickinson and Co., 1-12-cv-00275 (D. Del.), defendant Becton Dickinson previously challenged Enzo’s U.S. Patent No. 7,064,197 in two IPR proceedings (IPR2016-00820 and IPR2016-00822)[12] that resulted in Final Written Decisions in 2017 finding the challenged claims unpatentable. The ’197 patent relates to nucleic acid probes and microarrays.

In 2019, two years after the PTAB’s Final Written Decisions, Becton Dickinson filed two requests for EPR (90/014,270 and 90/90/014,272)[13] of additional claims of the ’197 patent, including claims 18 and 20 which were not challenged in the IPRs. The USPTO ordered reexamination and subsequently merged the two EPRs. In July 2022, while EPR 90/014,270 was still pending, Becton Dickinson filed another request for EPR (90/015,080), again challenging claims 18 and 20. The USPTO ordered reexamination and merged 90/015,080 with 90/014,270. In November 2025, the USPTO issued a reexamination certificate, confirming patentability of claims 18 and 20.

In December 2025, Becton Dickinson filed another request for EPR (90/015,749), re-challenging claims 18 and 20. The USPTO ordered reexamination in January 2026, and the case is still pending.

• In PH Health Ltd. v. Baxter Healthcare Corp., 1-25-cv-00861 (D. Del.), the patent at issue (U.S. Patent No. 11,207,280, which relates to epinephrine compositions) survived a first EPR and was subsequently challenged in a new EPR. During the litigation, in April 2025, an anonymous party filed an EPR of claims 1-3, 8, and 9 of the ’280 patent (90/019,939). The USPTO ordered reexamination, and in January 2026, issued a reexamination certificate confirming patentability of claims 1-3, 8, and 9.

In March 2026, an anonymous party filed a new request for EPR of the ’280 patent, re-challenging claims 1-6 and 9 (90/016,121). The USPTO ordered reexamination in April 2026, and the case is still pending.

Under General Plastic, serial challenges such as these would likely face steep discretionary denial hurdles at the PTAB. Not so at the CRU.

Settled Expectations:

Under the current discretionary denial framework in AIA proceedings, a patent owner’s “settled expectations” can weigh in favor of discretionary denial. As Acting Director Stewart stated in Dabico, “the longer the patent has been in force, the more settled expectations should be.”[14] The age of a patent is not an issue in EPRs. For example:

• Reexam nos. 90/015,776 and 90/016,373 both challenge Neurocentria’s U.S. Patent No. 8,637,061, which relates to magnesium compositions for neurological disorders. The ’061 patent issued in January 2014 and had been in force for nearly 12 years when the ’776 EPR was filed. The ’061 patent is asserted in Neurocentria Inc. v. Mando Int’l, LLC, 2-25-cv-05871 (C.D. Cal.).
• Reexam no. 90/019,884 challenges OMS Investments’s U.S. Patent No. 8,114,426, which relates to mesotrione compositions for controlling weed growth. The ’426 patent issued in February 2012 and had been in force for over 13 years when the EPR was filed. The ’884 patent is not currently involved in litigation.
• Reexam no. 90/019,810 challenges Rimfrost Technologies’s U.S. Patent No. 9,814,256, which relates to krill oil compositions and methods of producing the same. The ’256 patent issued in November 2017 and had been in force for over seven years when the EPR was filed. The ’256 patent is asserted in Rimfrost Tech. AS v. Aker BioMarine Antarctic US LLC, 1-25-cv-01559 (D. Del.).

Under Dabico and the current state of play at the PTAB, petitioners challenging these same patents in IPRs would need to grapple with the possibility of settled expectations. The age of the patent is not a factor in ordering EPRs.

3. EPR Can Be Used To Request a Stay of Parallel District Court Litigation

Although there is no statutory mandate to stay co-pending district court litigation once an EPR is ordered for a patent asserted in the litigation, district courts can and often do apply their inherent case-management authority to stay the litigation pending the outcome of the EPR. District courts typically evaluate stays under a three-factor test: (1) whether a stay will simplify the issues; (2) the stage of the litigation, including whether discovery is closed and a trial date is set; and (3) whether a stay would unduly prejudice or tactically disadvantage the non-movant.[15] Courts have emphasized that the “simplification” prong carries the most weight—reasoning that even without IPR-style estoppel, EPR can cancel, narrow, or amend claims, moot invalidity theories, and give the court the benefit of the USPTO’s expertise and a fully developed intrinsic record.[16]

Defendants can improve their odds of obtaining a stay by (i) moving early in the life of the parallel litigation, e.g., pre-Markman or before discovery has progressed significantly; (ii) filing EPRs on all (or substantially all) asserted patent claims; and (iii) waiting until the USPTO has actually ordered reexamination, rather than moving on a still-pending EPR request.

Of the EPRs we surveyed that involved parallel district court litigation, only one defendant has requested a stay pending EPR. In FMC Corp. v. Sharda USA, LLC, No. 24-cv-2419 (E.D. Pa.), Sharda USA requested a stay related to its EPR (Reexam nos. 90/016,336 and 90/16,0337), in May 2026. The court has yet to rule on Sharda’s motion.

4. EPR Can Potentially Impact Injunction Risk or Damages Awards in Litigation

In Jazz Pharmaceuticals, Inc. v. Avadel Pharmaceuticals, PLC, 1-21-cv-01594 (D. Del.), Jazz asserted U.S. Patent No. 11,147,782 against Avadel in November 2021. The ’782 patent relates to gamma-hydroxybutyrate (GHB) compositions. In August 2024, the court granted in-part Jazz’s motion for a permanent injunction. Avadel appealed that decision to the Federal Circuit. While the court’s permanent injunction decision was pending on appeal, an anonymous party filed a request for EPR of the ’782 patent in August 2025 (90/015,486).

While the EPR was filed anonymously, perhaps (if filed by Avadel) it was an attempt to invalidate the ’782 patent and potentially nullify the injunction. There is precedent for such a strategy. See e.g., ePlus, Inc. v. Lawson Software, Inc., 789 F.3d 1349 (Fed. Cir. 2015) (vacating district court’s injunction because it was based on a patent claim that the USPTO had since canceled via reexamination).

EPRs can also be considered after an unfavorable trial verdict to mitigate damages. If claims are canceled in the EPR before the damages judgment becomes final (i.e., no further appeals other than to the Supreme Court are possible), then the damages award can be vacated.[17] If the claims are amended before the damages judgment becomes final and are not substantially identical to the originally issued claims, the liable party can enjoy intervening rights that cut off damages from before the amended claims emerged from the EPR.[18]

5. Business Decision, Even When AIA Challenge Appears To Be a Viable Option

We identified several recent EPRs in TC1600 in which the circumstances—at least on the surface—appear to be less susceptible to PTAB discretionary denial arguments. And yet, the challengers nevertheless chose EPR over AIA challenge.

• Reexam no. 90/015,640 challenges ExxonMobil’s U.S. Patent No. 11,479,462. The ’462 patent issued in October 2022, and had only been in force for three years when EPR 90/015,640 was anonymously filed in October 2025. And the patent is not currently associated with any co-pending litigation.
• Reexam no. 90/015,660 challenges the U.S. Navy’s Patent No. 11,116,740. The ’740 patent, which relates to oral supplements comprising pentadecanoic acid for use in treating metabolic syndrome, was previously reexamined in 90/019,345. The ’345 reexam resulted in a reexamination certificate confirming patentability of amended and new claims. The reexamination certificate issued in December 2023, meaning the reexamined claims had only been in force for just under two years when EPR 90/015,660 was anonymously filed in November 2025. The ’740 patent is not currently associated with any co-pending litigation.
• Reexam no. 90/019,885 challenges Verve Therapeutics’s U.S. Patent No. 12,024,484. The ’484 patent relates to lipid formulations for gene editing, and issued in July 2024. Thus, the ’484 patent had only been in force for about eight months when the EPR was anonymously filed in March 2025. And there is no currently co-pending litigation of the ’484 patent.
• Reexam no. 90/019,830 challenges UPL Ltd.’s U.S. Patent No. 11,555,046, which relates to crystalline forms of L-glufosinate ammonium salt. The ’046 patent issued in January 2023, and had only been in force for two years when EPR 90/019,830 was anonymously filed in January 2025. There is no currently co-pending litigation of the ’046 patent.
• Reexam no. 90/016,178 challenges Microbiota Med’s U.S. Patent No. 12,329,738, which relates to urolithin A compositions for treatment of inflammatory skin conditions. The ’738 patent issued in June 2025, and had only been in force for ten months when EPR 90/016,178 was filed in April 2026. The ’738 patent is not currently involved in any co-pending litigation.
• Reexam no. 90/016,184 challenges Hansa Biopharma’s U.S. Patent No. 12,359,183, which relates to immunoglobulin (antibody)-cleaving cysteine proteases. The ’183 patent issued on July 15, 2025, and had been in force for nearly nine months (one day shy of the ’183 patent’s PGR eligibility expiration under 35 U.S.C. § 321(c)) when EPR 90/016,184 was filed on April 14, 2026. The ’183 patent is not currently involved in any co-pending litigation.

In these cases, each of the challenged patents has been in force for less than six years, which—according to Dabico[19]—weighs against a patent owner’s settled expectations. And none of these patents are associated with parallel litigation, meaning there presumably would not be issues of conflicting claim constructions (Revvo) or duplicative efforts between forums (Fintiv). Thus, numerous discretionary denial factors would appear to be in favor of an AIA petitioner. Why then file an EPR instead of an AIA challenge?

Perhaps it was simply a matter of cost. Perhaps it involved timing. Perhaps the requestor is a foreign sovereign (e.g., Tianma). Without knowing all of the facts, we can only speculate as to the impetus behind filing these reexaminations.

New Procedural Developments to Watch

On April 1, 2026, the USPTO announced that patent owners in EPR proceedings will be allowed to “provide information on why an argued teaching(s) in a request for reexamination would not raise a substantial new question of patentability.” Specifically, patent owners can now respond to a request for EPR before the Office determines whether to order reexamination and argue why the EPR does not raise a SNQ and, thus, should not be ordered.[20] The USPTO has cited the recent increase in EPR request volume as the reason for this new pre-order patent owner submission process, stating that it is straining the Office’s ability to make well-informed SNQ determinations within the statutory three-month window. Patent Owner’s also cannot use this new procedure make arguments that 35 U.S.C. § 325(d) should apply. Because the new pre-order paper procedure was adopted by rule waiver rather than rulemaking, the Office could modify or withdraw it in the future.

This change could affect requestor behavior at the margin by giving patent owners a new opportunity to shape the Office’s threshold view before reexamination is ordered. Whether that development will slow the recent growth in EPR requests—or instead simply change how requests are prepared—remains to be seen. Indeed, actions both patent owners and requesters should consider in view of this new procedure have been suggested by others at our firm.[21] And a review of the limited number of pre-order patent owner submissions filed to date suggests that patent owners are using the procedure selectively, primarily when they believe a focused threshold challenge could materially affect the SNQ determination.[22] Requestors are also routinely being denied requests to respond to pre-order patent owner submissions, suggesting that requestors should draft the EPR request with foreseeable pre-order patent owner submission arguments in mind.[23]

Additionally, the CRU recently denied at least three requests for EPR in view of a previous IPR challenge that was discretionarily denied by the Director.[24] The CRU’s basis for EPR denial was under 35 U.S.C. § 325(d), which states the Direct can reject a request for reexamination (or a petition for IPR or PGR) if “the same or substantially the same prior art or arguments previously were presented to the Office.” In the previous IPRs, the petitions did indeed assert the same prior art that the challenger asserted in the EPR. The Director, however, never reached the merits of the art in the IPR petitions as they were denied on discretionary bases. Thus, according to the Office, § 325(d)’s “arguments previously [ ] presented to the Office” does not require that the arguments were substantively considered by the Office. This new practice may be a signal from the Office that challengers need to pick either an IPR or an EPR, but not both.

Conclusion

EPR is plainly becoming a more important part of the patent-challenge landscape, including in the life sciences. For patent owners and challengers alike, EPR should be viewed not as a wholesale replacement for PTAB practice, but as a specialized tool whose value depends heavily on procedural posture and the circumstances of each case.

For practitioners in biotech and pharma, the practical takeaway is straightforward: when evaluating a validity challenge, EPR should be part of the standard forum-selection analysis. The key questions are no longer only whether the art is strong enough or whether litigation is pending. They also include whether an IPR is procedurally available, whether discretionary-denial risk is unacceptably high, whether a litigation milestone makes ex parte practice strategically useful, and whether the patent’s prosecution and challenge history creates room for a substantial new question of patentability. Those considerations—not abstract preferences for one forum or another—appear to be driving the use of EPRs in biotech and pharma.

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[1] See e.g., USPTO Memorandum on Interim Processes for PTAB Workload Management (March 26, 2025); USPTO Memorandum on Director Institution of AIA Trial Proceedings (Oct. 17, 2025); USPTO Memorandum on Additional Discretionary Institution Considerations (March 11, 2026).

[2] IPR2026-00097, Paper 17 (Director Decision, May 14, 2026) (precedential).

[3] IPR2020-00019, Paper 11 (PTAB, March 20, 2020) (precedential).

[4] IPR2016-01357, Paper 19 (PTAB, Sept. 6, 2017) (precedential).

[5] IPR2025-00632, Paper 20 (Director Decision, Nov. 3, 2025) (precedential).

[6] IPR2025-00408, Paper 21 (Act. Director Decision, June 18, 2025) (informative).

[7] IPR2025-00480, Paper 11 (Act. Director Decision, Sept. 4, 2025) (informative).

[8] IPR2025-01579, Paper 12 (Director Decision, March 18, 2026) (precedential).

[9] Jason D. Eisenberg, Jessica Harrison, and Patrick Murray, “Reexamination Statistics and the Federal Circuit’s SNQ Clarification/Expansion,” PTAB YEAR IN REVIEW 2023, available at https://www.sternekessler.com/app/uploads/2024/02/Reexamination-Statistics-and-the-Federal-Circuits-SNQ-Clarification-Expansion.pdf.

[10] See e.g., In re Gesture Technology Partners, LLC, 160 F.4th 1317 (2025) (holding that that the estoppel provision of § 315(e)(1) is inapplicable to an ongoing ex parte reexamination proceeding because at that point the challenger is no longer requesting or maintaining the proceeding.).

[11] IPR2016-01357, Paper 19 (PTAB, Sept. 6, 2017) (precedential).

[12] IPR2016-00820 and IPR2016-00822 were initially filed by Hologic, Inc. The PTAB joined Becton Dickinson to those proceedings as petitioner after BD filed copycat IPR petitions and motions for joinder.

[13] While many requests for EPR are filed anonymously via a strawman, these EPRs were filed “on behalf of Becton Dickinson.”

[14] Dabico, IPR2025-00408, Paper 21 at 2.

[15] See, e.g., Dental Monitoring v. Get-Grin Inc., No. 22-647, 2024 WL 1603403, at * 2 (D. Del. Apr. 9, 2024); Jiaxing Super Lighting Elec. Appliance Co., Ltd. v. All Star Lighting Supplies, Inc., No. 25-12390, slip op. at 8-9 (D.N.J. Apr. 24, 2026).

[16] See, e.g., Dental Monitoring, 2024 WL 1603403 at *5-*6 (citing cases); Jiaxing Super Lighting, slip op. at 14-15 (citing cases); WAG Acquisition LLC v. Flying Crocodile, Inc., No. 19-1278, 2021 WL 6693829, at *2-*3 (W.D. Wash. Dec. 28, 2021).

[17] Fresenius USA, Inc. v. Baxter Intern., Inc., 721 F.3d 1330, 1332 (Fed. Cir. 2013).

[18] 35 U.S.C. §§ 252, 307(b).

[19] Dabico, IPR2025-00408, Paper 21.

[20] “Pre-order Procedure regarding Substantial New Question determination in ex parte Reexamination Proceedings,” Official Gazette Notice, available at https://www.uspto.gov/sites/default/files/documents/og-preorder-snq-apr2026.pdf.

[21] Dohm Chankong, Ian Soule, Jacqueline Wright Bonilla, and Jason D. Eisenberg, “Part II: Déjà Vu at the CRU: Strategy Under the New Pre-Order Paper Procedure,” available at https://www.sternekessler.com/news-insights/insights/part-ii-deja-vu-at-the-cru-strategy-under-the-new-pre-order-paper-procedure/.

[22] Ryan M. Estatico, Jaqueline Wright Bonilla, and Jason D. Eisenberg, “Part III: Déjà Vu at the CRU: Early Lessons From the USPTO’s Patent Owner Pre-Grant Paper,” available at https://www.sternekessler.com/news-insights/insights/part-iii-deja-vu-at-the-cru-early-lessons-from-the-usptos-patent-owner-pre-grant-paper/.

[23] Ryan M. Estatico, Jason D. Eisenberg, and Jaqueline Wright Bonilla, “Part IV: Deja Vu at the CRU: Requester Responses, Improper Papers, and § 325(d): Early Front-End Principles in Ex Parte Reexamination,” available at https://www.sternekessler.com/news-insights/insights/part-iv-deja-vu-at-the-cru-requester-responses-improper-papers-and-%c2%a7-325d-early-front-end-principles-in-ex-parte-reexamination/.

[24] See 90/015,984 (denied in view of IPR2025-00928); 90/016,174 (denied in view of IPR2025-01526); and 90/015,967 (denied in view of IPR2024-00855).