Background
Norvasc® is a blockbuster blood-pressure drug manufactured by Pfizer whose active ingredient is amlodipine besylate — amlodipine in its benzene sulfonate (besylate) salt form. Pfizer held U.S. Patent No. 4,879,303, which claimed this specific salt form. Amlodipine itself had been disclosed in earlier prior art, but Pfizer argued that selecting the besylate salt was a non-obvious improvement because it provided superior stability, reduced clumping, and improved manufacturability compared to other salt forms.
When Apotex filed an Abbreviated New Drug Application (ANDA) seeking FDA approval to market a generic version of Norvasc, Pfizer sued for infringement under the Hatch-Waxman Act. The district court conducted a bench trial and upheld the patent’s validity, finding that Apotex had not shown by clear and convincing evidence that choosing the besylate salt would have been obvious. Apotex appealed.
The Court’s Holding
The Federal Circuit reversed, holding that the ‘303 patent was invalid for obviousness. The court found that a person of ordinary skill in pharmaceutical chemistry would have been motivated to test the besylate salt of amlodipine because the prior art — particularly the Berge reference, a comprehensive survey of pharmaceutical salts — identified besylate as one of the known, commercially acceptable salt forms. The court rejected Pfizer’s argument that besylate’s low frequency of use in prior marketed drugs (about 0.25% of drugs surveyed) made it an unexpected or non-obvious choice.
Applying the Supreme Court’s Graham v. John Deere framework and anticipating the KSR International v. Teleflex ruling issued the same month, the court emphasized that pharmaceutical salt selection is a routine, predictable process: chemists test a standard battery of salt forms when developing a drug candidate, and the besylate salt was within that routine toolkit. The modest commercial advantages Pfizer identified — better flow properties and tablet manufacturability — were predictable results of routine screening, not unexpected discoveries sufficient to overcome the prima facie case of obviousness.
Key Takeaways
- Selecting a known salt form of a previously disclosed drug is presumptively obvious if routine salt-screening methodology would have led a skilled chemist to test that form.
- Secondary considerations of commercial success cannot save a patent if the claimed subject matter was the result of routine, predictable pharmaceutical development rather than a genuine inventive leap.
- Low prior-art frequency of a particular salt form does not by itself establish non-obviousness — the question is whether skilled chemists would have been motivated to try it.
- The decision was a significant blow to so-called “evergreening” strategies — the pharmaceutical industry practice of obtaining new patents on salt forms or formulations of existing drugs to extend market exclusivity.
Why It Matters
The Pfizer v. Apotex ruling became a landmark in pharmaceutical patent law because it directly challenged one of the drug industry’s most common patent strategies: obtaining a separate, later-expiring patent on a specific salt form of an already-patented compound. The court’s willingness to invalidate a multi-billion-dollar patent protecting one of the best-selling drugs in the world sent a clear signal that the Federal Circuit would scrutinize salt-selection patents carefully.
For generic drug manufacturers and patients, the ruling represented a potential pathway to cheaper drugs sooner. For brand-name pharmaceutical companies, it reinforced the importance of demonstrating genuine unexpected advantages — not just incremental improvements — when seeking patent protection on drug formulations and derivatives. The case remains a touchstone in Hatch-Waxman ANDA litigation involving formulation and salt patents.