In 2003, the generics manufacturer Apotex filed an application to the FDA to market amlodipine besylate, the active ingredient in Norvasc, claiming that the Pfizer patent (US 4,879,303), which relates to the pharmaceutically active salts of amlodipine, was invalid for reasons of obviousness. In an earlier Pfizer patent (US 4,572,909) the company stated that the preferred amlodipine salt was maleate; however, as this salt had a problematic formulation, Pfizer switched to the beslyate salt, which was described as novel in the '303 patent (due to expire in September of this year following an additional 6-month paediatric exclusivity). Although lower courts ruled that the claims of the '303 patent were not anticipated by the earlier '909 patent, Apotex disagreed, stating that the use of the beslyate salt would be anticipated. Pfizer argued that because of the structure and rare use of this salt, there would have been no motivation to make the besylate formulation. However, the Court rejected this; ruling that the '303 patent claims would have been obvious as they represented an optimization process that stems from the “normal desire of scientists to improve upon what is already known”. Following this decision, Mylan — the first company to file for a generic drug application to make amlodipine besylate — has launched its generic product, in response to which Pfizer has announced that it will also launch a generic through its subsidiary Greenstone. Normally, Mylan would have enjoyed a 180-day marketing exclusivity under US patent law, but as the original Norvasc patent has expired, this no longer applies. Mylan has subsequently obtained an injunction preventing other companies from launching generics of Norvasc. This ongoing case presents questions involving the interaction between patent rights, paediatric exclusivity and 180-day generic exclusivity.
Pfizer Inc. versus Apotex Inc.:
http://www.fedcir.gov/opinions/06-1261.pdf
