It is not uncommon for a patentee that obtained a patent on a commercially successful pharmaceutical compound to attempt to strengthen its position by obtaining patents for related forms of the compound in order to prevent others from marketing the compound when the original patent expires.

Bristol-Myers Squibb (Bristol-Myers) obtained a patent on the chemical compound cefadroxil, an antibiotic effective against bacteria that are resistant to penicillin. This patent expired in 1987. Bristol-Myers also obtained a patent on a new crystalline form of cefadroxil known as Bouzard monohydrate. Zenith Laboratories (Zenith) sought to market cefadroxil DC which is a hemihydrate form of cefadroxil and differs structurally from Bouzard monohydrate.

Zenith filed a declaratory judgment action seeking a declaration that cefadroxil DC did not infringe the patent on Bouzard monohydrate.

Bristol-Myers conceded cefadroxil DC did not literally infringe its patent but argued that Zenith's product infringed under the doctrine of equivalents and Zenith's sale of cefadroxil DC would induce infringement because cefadroxil DC is converted to Bouzard monohydrate in the patient's stomach. The doctrine of equivalents argument was rejected by the District Court on the basis that the cefadroxil DC did not perform the same function as Bouzard monohydrate. The District Court, however, found that Zenith's sale of cefadroxil DC would induce infringement of the patent because the scientific evidence showed that cefadroxil DC converted to Bouzard monohydrate in the patient's stomach and that literal infringement of the Bouzard monohydrate patent occurs in a patient's stomach as a result of the ingestion of the cefadroxil DC.

On appeal, the Court of Appeals for the Federal Circuit affirmed the finding of no infringement under the doctrine of equivalents, but reversed the decision on inducement to infringe holding that the scientific evidence relied on by the District Court was not sufficient to establish that cefadroxil DC converted to Bouzard monohydrate in the patient's stomach.

This decision is to be compared with the Merrell Dow v. Norton case in the U.K which is discussed elsewhere in this Newsletter.