EPRx 101: Getting to Know Ex Parte Reexamination

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Ex parte reexamination (EPRx) is a powerful tool that allows any party — including the patent owner — to request that the United States Patent and Trademark Office (USPTO) reassess the validity of an issued patent based on prior art. EPRx can provide a cost-effective way to challenge a patent owned by an adverse party, before or after any litigation has been initiated. For a patent owner, EPRx gives the opportunity to strengthen a patent with amendments and the addition of new non-broadening claims. The threshold to initiate a reexamination is relatively low; under 35 U.S.C. § 303(a), a requester must demonstrate a “substantial new question of patentability” (SNQ) based on prior patents or printed publications. This prior art may include references already listed on the face of the patent or those that were not considered during prosecution of the patent.

EPRx invalidity grounds are limited to prior patents or printed publications, so challenges cannot be based on, for example, prior public use, system prior art, subject matter eligibility, indefiniteness, or inequitable conduct. (However, a patent owner can address these issues for their own patent through supplemental examination.)

Another distinctive feature of EPRx is that any party can initiate the proceeding. Third parties even have the option to do so anonymously, unlike in inter partes review (IPR,) where the real party in interest must be disclosed. Once reexamination is granted, a third party that requests reexamination generally is excluded from further participation, leaving the remainder of the process exclusively between the patent owner and the USPTO.

Also unlike IPR, EPRx does not have a strict deadline for filing. It may be requested at any time while the patent is enforceable, including after issuance and throughout its term, and typically up to six years after expiration.

EPRx timeline

Within three months of filing the EPRx request, the USPTO must determine whether the request demonstrates that there is an SNQ for any of the challenged claims. If the USPTO finds that an SNQ has been established, it issues an order for reexamination under 35 U.S.C. § 304 and initiates the EPRx proceeding.

Examination in an EPRx is handled by specialized examiners within the USPTO’s Central Reexamination Unit (CRU), and generally follows the framework of traditional patent prosecution, albeit with certain limitations, as shown in the flowchart below.

A significant restriction in EPRx is that the proceeding is typically limited to two office actions, and patent owners cannot prolong prosecution by filing a Request for Continued Examination. In rare cases, the CRU may reopen prosecution based on the patent owner’s response to the final office action.

Before the first office action, the patent owner may submit a patent owner statement and/or non-broadening preliminary claim amendments. If the patent owner files a statement, the requester may submit a reply, allowing the third-party requester one more chance to submit evidence and arguments in the proceeding.

If the patent owner disagrees with the final decision issued in reexamination, they may appeal to the Patent Trial and Appeal Board (PTAB), and from there, the U.S. Court of Appeals for the Federal Circuit.

The EPRx proceeding concludes when the CRU issues a Notice of Intent to Issue Ex Parte Reexamination Certificate, with a reexamination certificate issuing about two months later. The reexamination certificate details which claims have been cancelled as unpatentable, which have been confirmed as patentable (including new or amended claims), any statutory or terminal disclaimers filed, and which claims, if any, were not reexamined.

Key differences between EPRx and IPR

Patent challengers frequently compare EPRx and IPR to determine the most advantageous course of action. The two types of proceedings differ primarily in their level of adversarial engagement, procedural complexity, timing considerations, and estoppel implications, as shown in the chart below.

Overall, IPR generally is more structured and litigation-driven, with the petitioner and the patent owner both actively participating in the proceedings before the PTAB. In contrast, EPRx is an examiner-driven, non-adversarial process. Once an EPRx proceeding is initiated, third-party challengers typically have no further role.