Inter partes reviews (IPRs), post-grant reviews (PGRs) and ex parte reexaminations are all post grant proceedings offered by the United States Patent and Trademark Office (USPTO) that allow parties to challenge the validity of a patent.

Each procedure possesses its own advantages and considerations. To determine which to use, a challenger to the patent should consider several factors, such as the nature of the dispute, the availability of prior art, and the desired level of involvement from the owner or challenger.

Here are a few key differences:

1. Parties involved: In an IPR or PGR, a challenger files a petition to invalidate the claims of the patent, and both the challenger and the patent owner normally participate in the proceeding. The challenger must identify itself and all real parties in interest. In an ex parte reexamination, anyone can request reexamination of a patent and remain anonymous, but only the patent owner has the opportunity to participate in the reexamination process.
2. Standard for institution: In an IPR, the challenger must prove that there is a "reasonable likelihood” that the challenger will prevail with respect to at least one challenged claim. In a PGR, the standard is similar, but slightly higher. The PGR petition must demonstrate that it is “more likely than not” that at least one challenged claim is unpatentable. In an ex parte reexamination, the petition must demonstrate there is a substantial new question of patentability, which is a lower standard than the IPR and PGR standards.
3. Standard of review: In all three proceedings, the standard of review is whether at least one claim is more likely than not unpatentable. This standard of proving invalidity is easier to meet than the clear and convincing standard used in district court.
4. Timing: An ex parte reexamination may be requested at any time during the life of the patent. A PGR petition must be filed within the first nine months following the patent grant. An IPR petition may be filed any time after the nine-month mark following the patent grant, but must be filed within twelve months of being served with any complaint alleging infringement of that patent in U.S. district court.
5. Scope of petition’s grounds: In an IPR or ex parte reexamination, the petition is limited to anticipation and obviousness arguments based on patents and printed publications. While an ex parte reexamination can review grounds based on obviousness-type double patenting, IPRs and PGRs cannot since they are limited to statutory defenses of invalidity. A PGR has the widest scope of challenging the validity of the patent, as it is open to any statutory ground of invalidity under the patent statute (except best mode). That includes anticipation, obviousness, lack of written description, lack of enablement, indefiniteness and lack of patentable subject matter.
6. Scope of review: In an IPR and PGR, the scope of review is limited to the grounds asserted in the petition. In an ex parte reexamination, the USPTO can consider any prior art, even those independently found by the Patent Office and not the basis of request for reexamination, that raises a substantial new question of patentability.
7. PTAB involvement: IPR and post-grant proceedings are heard before the PTAB, while an ex parte reexamination is conducted by the USPTO's Central Reexamination Unit, which may thereafter be appealed to the PTAB.

For more information about post-grant proceedings, please contact Howard Suh at 212.878.7914 or hsuh@foxrothschild.com or another member of the firm’s national IP Litigation Practice Group.