Background
Purdue Pharma owned U.S. Patent No. 5,672,360 directed to methods of treating pain by administering an opioid analgesic (such as morphine) in a once-a-day controlled-release dosage form. The patent was related to the technology underlying OxyContin and similar extended-release opioid formulations. Faulding, a generic pharmaceutical company, sought to market its own once-daily morphine product and challenged the ‘360 patent as invalid.
The specific claim limitation at issue required that the controlled-release formulation produce a maximum plasma concentration (Cmax) that was “more than twice” the plasma level of the drug at 24 hours after administration (C24). This ratio — Cmax more than twice C24 — was not expressly described in the patent’s original application as filed. Rather, Purdue had added this limitation during prosecution to distinguish prior art.
Faulding argued that the ‘360 patent lacked adequate written description under 35 U.S.C. § 112 because the original disclosure did not demonstrate that the inventors had possession of a formulation specifically characterized by the Cmax/C24 ratio. Purdue countered that the pharmacokinetic data already in the original specification implicitly supported that ratio. The district court agreed with Faulding and invalidated the claims.
The Court’s Holding
The Federal Circuit affirmed. Writing for the court, Judge Bryson held that the written description requirement demands that the specification demonstrate the inventors actually had possession of the claimed invention at the time the application was filed — not merely that the claimed feature could be derived by subsequent analysis of existing data. Where a claim limitation is “not discussed even in passing” in the original disclosure, adding it during prosecution constitutes the type of overreaching the written description requirement was designed to prevent.
The court acknowledged that the original specification contained pharmacokinetic data, but those data did not specifically disclose the Cmax/C24 ratio as a characteristic of the invention. Purdue was, in effect, trying to pick a specific tree out of the forest — selecting one particular parameter relationship after the fact to describe an invention that had never been claimed in those specific terms originally.
The decision reinforced a broader principle: the written description requirement is not satisfied merely by showing that the original specification contains data from which a skilled artisan might derive the claimed limitation. The inventors must themselves have “indicated” possession of the precise claimed subject matter.
Key Takeaways
- The written description requirement requires that the original specification actually describe the invention as claimed — including specific limitations added during prosecution — not merely enable a person of skill to figure it out from the data.
- Applicants cannot add new claim limitations during prosecution that characterize the invention in ways not indicated in the original filing, even if such limitations might be derivable from the original data.
- “Picking a tree out of the forest” — selecting one specific parameter relationship from a broad disclosure of data — does not satisfy the written description requirement for a claim limited to that specific parameter relationship.
- Pharmacokinetic ratios and formulation characteristics that define the invention must be described as inventive features in the original specification, not merely demonstrated in the data.
- This principle applies equally in biotech, chemistry, and pharmaceutical patent applications, where inventors may be tempted to add claim limitations based on post-filing insights into their own data.
Why It Matters
Purdue Pharma v. Faulding addressed a common pharmaceutical patent prosecution strategy: filing broad applications and then adding specific claim limitations during prosecution to distinguish prior art, after recognizing which formulation characteristics are competitively valuable. The Federal Circuit’s decision limits this practice by enforcing the written description requirement as a safeguard against overreaching by applicants who seek to claim more than they disclosed.
The decision remains a significant authority in pharmaceutical patent litigation, particularly in Hatch-Waxman cases where brand manufacturers often rely on continuation patents with refined claim limitations that were not part of the original disclosure. It also illustrates that even patentees with commercially important innovations — here, the controlled-release opioid technology that generated enormous revenues — are not immune to invalidity when the patent prosecution strays beyond the original invention as described.