Federal Circuit Upholds Patent Invalidation of Merck's Oral Cladribine MS Treatment Regimen
Key Insights
The U.S. Court of Appeals for the Federal Circuit affirmed PTAB decisions invalidating Merck Serono (search)'s patents covering oral cladribine dosing regimens for multiple sclerosis (search) treatment.
The court ruled that prior art references describing similar multi-phase cladribine regimens with drug-free intervals rendered Merck's patents obvious.
The decision establishes important precedent for joint inventorship in patent law, requiring identical inventive entities to exclude prior art as "one's own work."
The U.S. Court of Appeals for the Federal Circuit delivered a significant blow to Merck Serono S.A. (search)'s intellectual property portfolio on October 30, 2025, affirming Patent Trial and Appeal Board (PTAB) decisions that invalidated key patents protecting the company's oral cladribine treatment regimen for multiple sclerosis (search). The ruling addresses both substantive patent law and establishes important precedent regarding when disclosures with overlapping inventors qualify as prior art.
Patent Challenge and Claims
The consolidated appeals arose from PTAB's final written decisions in IPR2023-100480 and IPR2023-100481, where Hopewell Pharma Ventures (search) successfully challenged claims in U.S. Patent Nos. 7,713,947 and 8,377,903. Both patents cover a multi-phase oral cladribine regimen comprising an induction period, an extended drug-free period, and a maintenance retreatment period for treating multiple sclerosis (search).
Representative claim 36 of the '947 patent specifies an induction period lasting about 2-4 months with a total cladribine dose of about 1.7-3.5 mg/kg, followed by about 8-10 months without cladribine, followed by a 2-4 month maintenance period with a total cladribine dose of about 1.7 mg/kg, and then another drug-free interval. The '947 patent lists four Serono (search) scientists as inventors: Drs. De Luca, Ythier, Munafo, and Lopez-Bresnahan.
Development Background and Prior Art
The challenged patents emerged from a joint development effort that began in 2002 between Serono (search) (acquired by Merck in 2006) and IVAX (search), aimed at formulating an oral cladribine product to treat MS. Scientists from both companies exchanged confidential information during development, with Serono circulating a "Briefing Document" in December 2003 outlining a draft regimen involving repeated short daily dosing blocks separated by prolonged drug-free periods.
The PTAB found the claims unpatentable as obvious over a combination of two key references: an international application published in 2004 by Bodor and Dandiker describing an oral cladribine-cyclodextrin complex with specific dosing schedules, and a 1998 clinical paper by Stelmasiak reporting relapse rate reduction following cladribine treatment in cyclical courses with drug-free intervals.
The Bodor reference contained what parties termed the "six-line disclosure," specifying daily 10 mg doses for five to seven days in each of two months, followed by ten months of no treatment. The 1998 Stelmasiak reference taught oral or subcutaneous cladribine administered in monthly five-day courses across six months, followed by additional courses at extended intervals with intervening drug-free intervals, documenting lymphocyte suppression and relapse reduction.
Joint Inventorship and Prior Art Doctrine
A critical legal issue addressed by the Federal Circuit concerned whether Bodor's disclosure qualified as prior art "by another" under pre-AIA § 102(e). Merck argued that because at least one inventor named on its patents (particularly Dr. De Luca) contributed to the dosing regimen reflected in Bodor's six-line disclosure, the reference embodied "the inventors' own work" and should be excluded from prior art.
The Federal Circuit rejected Merck's legal theory, clarifying that under longstanding precedent including In re Land, a disclosure is excluded from prior art only when it reflects the work of the same inventive entity as the later patent. For joint inventorship, the relied-on portions of the earlier disclosure must reflect the collective work of the same joint inventors named on the later patent. Any incongruity—whether subtracting or adding inventors—renders the earlier disclosure "by another."
The court held that the PTAB permissibly required Merck to produce corroborated evidence showing that the relied-on Bodor disclosure reflected an inventive contribution from all named inventors on Merck's challenged patents. Merck failed to do so, particularly regarding Dr. De Luca's specific, significant contribution to the six-line regimen.
Obviousness Analysis
Having established Bodor as prior art, the Federal Circuit held that substantial evidence supported the PTAB's obviousness determination. The PTAB found that Bodor taught the claimed induction phase and extended cladribine-free period, and that a person of ordinary skill would have been motivated to follow Bodor's express guidance and implement a maintenance retreatment phase given MS's chronic nature and cladribine's documented effects.
Stelmasiak's clinical study reinforced the retreatment concept, teaching cladribine re-administration after drug-free intervals in remitting-relapsing MS patients and providing efficacy evidence. The PTAB credited expert testimony that Bodor's specification of a finite drug-free period logically implies retreatment for a chronic disease, and that practitioners would use Bodor's initial dosing as a starting point for maintenance-phase optimization.
The court rejected Merck's contention that the claims require automatic retreatment regardless of safety or disease progression, observing that the claims do not impose such a condition. The record established a reason to combine the references with reasonable expectation of success, supported by Bodor's and Stelmasiak's efficacy data and the ability to empirically tune dosing.
Implications for Pharmaceutical Patents
The Federal Circuit's decision offers two significant takeaways for pharmaceutical patent law. First, it clarifies the pre-AIA "by another" doctrine in joint inventorship contexts, establishing that overlapping inventors do not suffice to exclude prior art—identity of the inventive entity is the touchstone, requiring strong, corroborated proof of joint inventive contribution to specific content.
Second, the ruling underscores the PTAB's and Federal Circuit's pragmatic approach to obviousness in pharmaceutical dosing regimen cases. Where prior art discloses similar treatment paradigms, documented efficacy, and explicit statements that dosing can be empirically optimized, courts may conclude that combining references and optimizing prior art regimens to arrive at claimed inventions falls within ordinary skill in the art.