Post-Grant Review (PGR) and Inter Partes Review (IPR): Strategies for Patent Invalidation

February 24, 2025
- Intellectual Property (IP)
- Invalidation

1. Introduction

Patent validity is not always guaranteed, even after a patent is granted by the United States Patent and Trademark Office (USPTO). Many patents contain overly broad claims, insufficient descriptions, or prior art conflicts, making them susceptible to invalidation. Two of the most effective tools for challenging and invalidating patents in the U.S. are Post-Grant Review (PGR) and Inter Partes Review (IPR), both introduced under the America Invents Act (AIA) of 2011.

These administrative trials provide an efficient, cost-effective alternative to traditional patent litigation, reducing the financial burden on companies and mitigating risks of infringement disputes.

2. Understanding Post-Grant Review (PGR) and Inter Partes Review (IPR)

While both PGR and IPR provide a pathway for challenging patents, they differ significantly in timing, grounds for challenge, and procedural rules.

What is Post-Grant Review (PGR)?

PGR allows a third party to challenge a patent within the first nine months after its grant. It provides broad grounds for invalidation, making it the most comprehensive post-grant challenge mechanism available.

Key Features of PGR:

Timing: Must be filed within nine months of patent issuance.
Grounds for Challenge: Can be based on any ground of invalidity, including:
- §101 (subject matter eligibility).
- §102 (novelty).
- §103 (obviousness).
- §112 (lack of written description, indefiniteness, or enablement).
Burden of Proof: Petitioner must show that at least one claim is more likely than not invalid.
Who Can File?: Any third party, including competitors, investors, and public interest groups.
Duration: PGR proceedings are typically completed within 12-18 months after institution.

Best Used When:

The patent is newly granted, and there is clear evidence of invalidity.
The patent fails to describe the invention properly (Section 112 challenge).
The invention covers abstract ideas or lacks novelty (Section 101 or 102 challenge).

What is Inter Partes Review (IPR)?

IPR is another post-grant challenge, but unlike PGR, it is only available after the first nine months of a patent’s issuance. It is limited to prior art-based challenges under §102 (novelty) and §103 (obviousness) using patents or printed publications.

Key Features of IPR:

Timing: Can be filed after the nine-month PGR window closes or after PGR concludes.
Grounds for Challenge: Can be based on any ground of invalidity, including:
- §102 (novelty based on prior patents or publications).
- §103 (obviousness based on prior patents or publications).
- Cannot challenge a patent under §101 (subject matter eligibility) or §112 (written description or enablement).
Burden of Proof: Petitioner must show that at least one claim is more likely than not invalid.
Who Can File?: Any third party, including competitors or industry watchdogs.
Duration: Typically completed in 12-18 months after institution.

Best Used When:

New prior art has been discovered that was not considered during the examination.
A patent contains broad or vague claims that lack novelty.
The goal is to remove an infringement threat efficiently without costly litigation.

3. Key Differences Between PGR and IPR

Feature	Post-Grant Review (PGR)	Inter Partes Review (IPR)
Filing Window	Within 9 months of patent issuance	After 9 months of patent issuance
Grounds for Challenge	§101, §102, §103, §112 (subject matter, novelty, obviousness, written description, enablement)	§102, §103 (novelty and obviousness based on patents/publications only)
Burden of Proof	More likely than not invalid	Reasonable likelihood of unpatentability
Final Decision Timeline	12-18 months	12-18 months
Usage Preference	Best for early-stage, broad challenges	Best for prior art-based invalidation

4. Why Businesses Use PGR and IPR for Patent Invalidation

With the rising costs of patent litigation (averaging $2.5 million to $4 million for high-stakes cases), companies are increasingly turning to PGR and IPR as cost-effective alternatives. The Patent Trial and Appeal Board (PTAB) resolves most cases within 18 months, compared to multi-year federal court litigation.

Advantages of PGR and IPR Over Traditional Litigation:

✅ Cost Savings: PGR/IPR costs range between $300,000 – $600,000, significantly lower than court litigation.
✅ Speed: Resolves disputes in 12-18 months, whereas federal litigation takes 3-5 years.
✅ Higher Success Rate: Statistics show that 75-80% of patents challenged via IPR result in claim cancellation or modification.
✅ Reduced Legal Complexity: No jury trials—cases are decided by the USPTO’s Patent Trial and Appeal Board (PTAB).

5. Common Misconceptions About PGR and IPR

🚫 “PGR/IPR are only for large corporations.”

False. Even startups and SMEs frequently use these proceedings to challenge competitors’ patents and clear market entry barriers.

🚫 “Once a patent is challenged in PGR/IPR, it is automatically invalidated.”

False. The burden of proof is on the petitioner, and not all challenges succeed. The PTAB evaluates evidence rigorously.

🚫 “IPR can challenge all aspects of a patent.”

False. IPR is strictly limited to §102 and §103 (prior art challenges) and cannot be used for subject matter eligibility disputes.

6. Strategies for Successful Patent Invalidation Using PGR and IPR

Challenging a granted patent requires a well-prepared strategy, strong prior art, and legal expertise. Below are key approaches to maximize the chances of invalidating a patent through these proceedings.

1. Prior Art Search – The Foundation of a Strong Challenge

A well-executed prior art search is critical for IPR and still highly valuable for PGR. It helps identify existing patents, publications, or technical papers that invalidate the granted patent’s claims.

How to Strengthen Your Case with Prior Art:
✅ Use AI-driven tools like PatDigger LLM or XLSCOUT’s Novelty Checker to discover previously overlooked prior art.
✅ Identify foreign patents and non-patent literature that the examiner may have missed.
✅ Find expired patents with similar claims to argue lack of novelty.

Example:

In Google v. Personal Audio LLC (IPR2014-00070), Google successfully invalidated Personal Audio’s podcasting patent by citing a 1996 patent application that predated the claims, proving lack of novelty.

2. Target Weak Patent Claims & Overly Broad Language

Patents with broad, ambiguous claims are easier to challenge under both PGR and IPR.

Best Practices:
✅ Focus on functional claim language that lacks specificity.
✅ Identify claims that do not explicitly define a novel feature.
✅ Use expert declarations to show how the claims are obvious to a skilled person in the field.

Example:

In Apple v. VoIP-Pal (IPR2016-01201), Apple argued that VoIP-Pal’s broad voice-over-internet patents covered generic functions already known in prior art. The PTAB ruled that the claims were too broad, leading to invalidation.

3. Exploit Section 112 Challenges in PGR

Since PGR allows challenges under §112 (written description and enablement), it’s a powerful strategy against patents with insufficient disclosure.

Key Targets:
✅ Claims that lack sufficient technical description to enable reproduction.
✅ Overclaimed patents where the specification does not fully support all claims.

Example:

In Momenta Pharmaceuticals v. Bristol-Myers Squibb (PGR2018-00033), the PTAB ruled that BMS’s anticoagulant drug patent lacked adequate written description, invalidating key claims.

4. Use Technical & Economic Expert Testimony

Expert technical declarations and economic analysis can provide strong evidence to support patent invalidation.

How to Use Expert Testimony:
✅ Show how the claims overlap with known technologies.
✅ Use economic impact analysis to demonstrate that enforcing the patent would create an unfair monopoly.

Example:

In Samsung v. Smartflash (IPR2015-00056), Samsung leveraged multiple expert reports to prove that Smartflash’s patents on digital rights management were obvious based on prior patents, leading to their invalidation.

5. File IPR to Challenge Competitor Patents and Avoid Infringement Risks

Companies often use IPR strategically to eliminate competitor patents before entering the market.

Best Practices:
✅ Conduct freedom-to-operate (FTO) searches to identify patents that could block your product.
✅ File IPR before potential litigation, reducing legal risks.
✅ Monitor competitor patent filings and challenge them proactively.

Example:

In Ford v. Paice LLC (IPR2015-00758), Ford preemptively challenged hybrid vehicle patents owned by Paice, reducing infringement risks before launching its own hybrid models.

7. Key Takeaways for Businesses and Patent Professionals

✅ 1. PGR is best for early-stage, broad challenges.

Ideal when patents have overly broad claims, weak descriptions, or subject matter issues.

✅ 2. IPR is the preferred tool for prior art-based challenges.

Best for invalidating patents based on novelty and obviousness using existing patents/publications.

✅ 3. Prior art search is critical.

AI-driven patent analytics tools can uncover hidden prior art and strengthen challenges.

✅ 4. Expert testimony strengthens the case.

Courts rely heavily on technical and economic expert reports to determine obviousness and enablement.

✅ 5. PGR/IPR should be part of a broader IP strategy.

Companies should monitor competitor patents proactively and use these tools to mitigate infringement risks.

8. Conclusion: The Power of PGR and IPR in Patent Disputes

Both PGR and IPR serve as valuable tools for patent invalidation, allowing businesses to remove weak patents, challenge competitors’ IP, and strengthen their market position. The strategic use of prior art, expert testimony, and Section 112 challenges can make the difference between a successful invalidation or a missed opportunity.

By leveraging these proceedings, companies can avoid costly infringement lawsuits, block competitors from enforcing weak patents, and ensure freedom to operate in key markets.