Senju Pharmaceutical Co., Ltd. v. Lupin Ltd.

Case Name: Senju Pharmaceutical Co., Ltd. v. Lupin Ltd., Civ. No. 11-271-SLR (Consol.), 2012 U.S. Dist. LEXIS 173595 (D. Del. Dec. 7, 2012) (Robinson, J.)

Drug Product and Patent(s)-in-Suit: gatifloxacin and disodium edetate; U.S. Pat. Nos. 6,333,045 (“the ’045 patent”) and 5,880,283 (“the ’283 patent”)

Nature of the Case and Issue(s) Presented: Plaintiffs filed a complaint against Lupin alleging infringement of the ’045 and ’283 patents. On May 23, 2011, plaintiffs amended their complaint, adding that plaintiffs Senju and Kyorin had filed a request for reexamination of claims 1-3, 6, 8 and 9 of the ’045 patent. Lupin filed an answer and counterclaim on June 6, 2011. Plaintiffs filed an answer to the counterclaim on June 27, 2011. On November 21, 2011, plaintiffs filed two second amended complaints based on alleged infringement of the ‘045 patent as reexamined. Currently before the court is Lupin’s motion for judgment on the pleadings.

The issue presented was whether Lupin was entitled to a judgment on the pleadings for invalidity of the reexamined claims of the ’045 patent. In a prior litigation between Senju and Lupin, the district court found the claims of the ’045 patent invalid on the basis of obviousness. The claims included a limitation that the EDTA concentration was between 0.001 and 0.2 w/v%. The reexamined claims of the ’045 patent contained a limitation that EDTA concentration was limited to 0.01 w/v%.

Lupin argued that the reexamined claims are invalid under collateral estoppel because the issues in the prior case are the same as the present case, namely whether the prior art taught having EDTA at 0.01 w/v%. Plaintiffs argued that the issues were different and that they did not have a fair and full opportunity to litigate the issue of whether the prior art invalidates the reexamined claims with this new limitation. The court denied Lupin’s motion.

Why Plaintiffs Prevailed: The district court denied Lupin’s motion because the court did not, in the prior proceeding, make a specific finding of whether the prior art taught the new limitation of 0.01 w/v% of EDTA. The court stated that plaintiffs did not have a full and fair opportunity to argue why claims with this new limitation were valid. Moreover, the court did not believe that Lupin showed sufficient evidence that the new limitation does not lend patentable significance to the reexamined claims.  Thus, the court denied Lupin’s motion.