Purdue Pharma LP v. Depomed Inc

1. Case Identification

• Case #: IPR2014-00379
• Patent #: 6,340,475
• Filed: January 24, 2014
• Petitioner(s): Purdue Pharma L.P.
• Patent Owner(s): Depomed, Inc.
• Challenged Claims: 43, 54, 55, 57, 58, and 66

2. Patent Overview

• Title: Controlled Release Oral Drug Dosage Form
• Brief Description: The ’475 patent describes a method for administering a controlled-release oral dosage form designed for gastric retention. The technology involves a solid polymeric matrix that swells in gastric fluid, promoting retention in the stomach when a patient is in a "fed mode," thereby extending the drug's release time in an acidic environment.

3. Grounds for Unpatentability

Ground 1: Anticipation by the ’837 Patent - Claims 43, 57, and 58 are anticipated by the ’837 patent.

• Prior Art Relied Upon: Shell (’837 patent; Patent 5,582,837).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner argued that the ’837 patent explicitly discloses every element of claim 43. The ’837 patent teaches a sustained-release oral dosage form for administration to a patient in a "fed mode" to promote gastric retention. It discloses a swellable polymer matrix that remains intact, releases a drug over a prolonged period, and retains at least 40% of the drug after one hour while releasing substantially all of it within about ten hours. The ’837 patent also discloses drugs with ionized groups in the pH 5-8 range and specifies drug-to-polymer weight ratios that overlap with those claimed. For dependent claims 57 and 58, the ’837 patent explicitly discloses the use of alkyl-substituted celluloses, including hydroxypropylmethyl-cellulose (HPMC), as the polymeric matrix.

Ground 2: Anticipation by the ’803 Patent - Claims 43, 54, 55, 57, 58, and 66 are anticipated by the ’803 patent.

• Prior Art Relied Upon: Shell et al. (’803 patent; Patent 6,120,803).
• Core Argument for this Ground:
  • Prior Art Mapping: Petitioner asserted that the ’803 patent, which was not before the Examiner during prosecution, discloses all limitations of the challenged claims. The ’803 patent describes a gastric retentive dosage form adapted to swell in the stomach, comprising a polymer matrix with a dispersed drug, and specifies administration to a subject in a fed state. Figure 12 of the ’803 patent shows a release profile where the dosage form retains about 80% of the drug after one hour and releases it over ten hours. The ’803 patent further teaches the use of poly(ethylene oxide) (PEO) with a molecular weight between 5,000,000 and 8,000,000, anticipating claims 54 and 55. It also discloses HPMC with viscosity ranges that anticipate claim 66 and other alkyl-substituted celluloses for claims 57 and 58.

Ground 3: Obviousness over ’837 Patent, Baveja, and Colombo - Claims 43, 57, and 58 are obvious over the ’837 patent in view of Baveja and Colombo.

• Prior Art Relied Upon: ’837 patent, Baveja (a 1987 journal article on hydrophilic matrix tablets), and Colombo (a 1990 journal article on drug release modulation).

• Core Argument for this Ground:

  • Prior Art Mapping: Petitioner contended that even if not anticipated, the claims would have been obvious. The ’837 patent provides the foundational teaching of a swellable, gastric-retentive dosage form for administration in a fed mode. Baveja and Colombo, which were also not before the Examiner, teach specific HPMC-based formulations with drugs (alprenolol HCl and diltiazem HCl) that have ionized groups in the required pH range. These references disclose drug-to-polymer ratios, release kinetics, and tablet integrity properties that are substantially the same as those claimed in the ’475 patent. Petitioner’s expert declaration included test results confirming that formulations made according to Baveja’s teachings exhibit the claimed swelling and drug release properties.
  • Motivation to Combine: A POSITA would combine these references to solve the known problem of formulating a swellable, controlled-release dosage form for gastric retention. The teachings are interrelated, as all three references focus on HPMC-based matrix tablets for controlled drug delivery. A POSITA would naturally look to articles like Baveja and Colombo to optimize the specific formulation parameters (e.g., release kinetics, tablet integrity) of the general system taught in the ’837 patent.
  • Expectation of Success: A POSITA would have had a high expectation of success because combining these teachings involved using well-known polymers (HPMC) with known drugs to achieve predictable results in drug release and tablet swelling, which were routine formulation activities at the time.

• Additional Grounds: Petitioner asserted additional obviousness challenges, including grounds that claims 54 and 55 are obvious over the ’837 patent in view of the ’125 patent (teaching PEO) and that claim 66 is obvious over the ’837 patent in view of Colombo (teaching specific HPMC viscosity). Further grounds argued that all challenged claims are obvious over the ’803 patent in view of Baveja and Colombo.

4. Key Claim Construction Positions

• "gastric fluid": Petitioner adopted a construction from prior district court litigation, defining the term as "[b]oth the fluid in the stomach and simulated or artificial fluids recognized by those skilled in the art as a suitable model for the fluid of the human stomach."
• "releases substantially all of said drug within about ten hours": For the purposes of the petition, Petitioner proposed construing this phrase, as set forth in claim 43, to mean "at least 80% of the drug has been released after ten hours of immersion in gastric fluid," based on intrinsic evidence and constructions of similar terms in related patents.

5. Relief Requested

• Petitioner requests institution of inter partes review and cancellation of claims 43, 54, 55, 57, 58, and 66 of the ’475 patent as unpatentable under 35 U.S.C. §102 and §103.