Pfizer Inc. v. Apotex, Inc.
480 F.3d 1348 (2007)
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Rule of Law:
A patent claim for a new chemical formulation is invalid for obviousness if the prior art suggests a finite and identified set of potential candidates to solve a known problem, and there is a reasonable expectation of success in testing those candidates, even if some routine experimentation is required to verify the optimal choice.
Facts:
- Pfizer invented the active ingredient amlodipine and secured U.S. Patent No. 4,572,909 ('909 patent), which disclosed that the drug could be combined with various pharmaceutically-acceptable anions to form salts, with maleate being the preferred salt.
- During the development of a commercial tablet, Pfizer scientists discovered that the amlodipine maleate salt formulation was chemically unstable and had poor processing characteristics, specifically stickiness, which made tablet manufacturing difficult.
- To resolve these issues, a Pfizer scientist, Dr. James Wells, proposed testing a small group of seven alternative anions to form a new salt, one of which was benzene sulphonate (besylate).
- Subsequent testing by Pfizer scientists revealed that the amlodipine besylate salt exhibited superior stability and was significantly less sticky than the maleate salt.
- Based on these superior physicochemical properties, Pfizer selected amlodipine besylate for its commercial product, Norvasc®, and filed for a new patent on this specific salt form, which issued as U.S. Patent No. 4,879,303 ('303 patent).
Procedural Posture:
- Pfizer Inc. filed a patent infringement suit against Apotex, Inc. in the U.S. District Court for the Northern District of Illinois.
- Apotex filed a counterclaim seeking a declaratory judgment that Pfizer's '303 patent was invalid for obviousness and unenforceable for inequitable conduct.
- Apotex stipulated that its generic drug would infringe the '303 patent if the patent was held valid and enforceable.
- After a bench trial, the district court ruled in favor of Pfizer, finding the '303 patent was not invalid and not unenforceable.
- The district court enjoined Apotex from marketing its generic product before the '303 patent expired.
- Apotex, as appellant, appealed the district court's judgment to the U.S. Court of Appeals for the Federal Circuit.
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Issue:
Is U.S. Patent No. 4,879,303, which claims the besylate salt of amlodipine, invalid for obviousness under 35 U.S.C. § 103(a) in light of prior art disclosing amlodipine, its pharmaceutically-acceptable salts, and the properties of the besylate anion?
Opinions:
Majority - Michel, Chief Judge
Yes. U.S. Patent No. 4,879,303 is invalid for obviousness because the prior art provided a clear motivation and a reasonable expectation of success for a person of ordinary skill to create the besylate salt of amlodipine to solve known formulation problems. The court reasoned that the prior '909 patent taught the creation of pharmaceutically-acceptable salts of amlodipine. When Pfizer encountered stability and stickiness problems with its preferred maleate salt, a person of ordinary skill in the art would have been motivated to look at other known, FDA-approved anions, such as the 53 listed in the prior art Berge article. Other prior art references (Schmidt, Spiegel, Carabateas) further suggested that besylate salts had desirable properties for pharmaceutical formulations. Therefore, selecting besylate from this small, defined group of candidates to solve the specific problems encountered was not an inventive step but rather routine optimization. The court held that absolute predictability is not required for obviousness; a reasonable expectation of success is sufficient. The improvements shown by the besylate salt were not sufficiently 'unexpected' to overcome this strong prima facie case of obviousness.
Analysis:
This case significantly clarifies the boundary between a patentable invention and an 'obvious to try' experiment in pharmaceutical patent law. The court's holding suggests that patenting a new salt form of a known drug is difficult when the prior art already identifies a limited number of known, viable options to solve a specific problem. This decision makes it harder for pharmaceutical companies to extend patent monopolies through 'evergreening' strategies involving minor formulation changes. It establishes that routine optimization, even if it leads to a superior commercial product, does not rise to the level of a non-obvious invention if the path to that optimization was clearly suggested by the prior art.
