Eisai Wins Preliminary Injunction Against Teva's Generic Altheimer's Drug

Includes: ESALY, TEVA
by: Aaron F. Barkoff

Eisai Co., Ltd. (OTCPK:ESALY), the Japanese manufacturer of Aricept (donepezil hydrochloride), has won a preliminary injunction against Teva Pharmaceuticals USA, Inc. (NYSE:TEVA), keeping Teva's generic version of Aricept off the market for the time being. Aricept, which accounts for $1.6 billion in annual U.S. sales, is reportedly the world's most prescribed treatment for Alzheimer's disease.

In the decision (pdf file), released Friday, the district court found that Eisai is likely to succeed on its claim of infringement because Teva's sole defense, that U.S. Patent No. 4,895,841 is unenforceable for inequitable conduct, lacks substantial merit. Initially, Teva also asserted that the '841 patent is invalid for obviousness. However, in December, Teva acknowledged that it had dropped its obviousness defense. Teva stipulated to infringement of claims 8, 10 and 13 of the '841 patent, which are directed to the active ingredient in Aricept, donepezil hydrochloride, pharmaceutical compositions thereof, and a method for treating Alzheimer's disease by administering the compound.

Teva asserted that the '841 patent is unenforceable for inequitable conduct due to Eisai's failure to disclose two references during prosecution: a co-pending patent application owned by Eisai, now known as the '431 patent; and a 1984 article in the Journal of Medicinal Chemistry, authored by Richard A. Kenley. According to Teva, had Eisai informed the Examiner of the '431 patent application and the Kenley article, the Examiner likely would have rejected the '841 patent application for obviousness-type double patenting over the '431 patent. Donepezil is an acetylcholinesterase ("AChE") inhibitor. The '431 patent is directed to AChE inhibitor compounds that are structurally related to donepezil, while the Kenley article focuses on restoring activity to already-inhibited AChE enzymes.

The court determined that "Eisai's co-pending '431 patent was material enough that it should have been disclosed," noting that "both patent applications were largely aimed at treating the same disease, Alzheimer's, and both patent applications stemmed from research by at least nine common inventors at Eisai." However, after carefully comparing the chemical structures of donepezil and the compounds disclosed by the '431 patent, the court concluded that the materiality of the '431 patent is "very low." Meanwhile, the court concluded that the materiality of the Kenley article is "almost non-existent." Dr. Kenley himself submitted a declaration in support of Eisai.

With respect to the other prong inequitable conduct, the court stated: "there can be no punishable intent to deceive where there is no substantial likelihood that a reasonable patent examiner would have considered the undisclosed information important to deciding whether to allow the application to issue as a patent." Accordingly, the court concluded that Eisai is likely to succeed on the merits of its case at trial. The court treated the remaining elements of the preliminary injunction analysis in summary fashion.

A trial date in the case has not been set. The '841 patent is set to expire November 25, 2010. Assuming that Teva holds the 180-day exclusivity rights for generic Aricept, Teva will likely proceed to trial (and appeal, if necessary), hoping for a decision declaring the '841 patent unenforceable at least six months prior to then.


  • Bloomberg article
  • Eisai press release
  • Teva press release