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Rewriting Dependent Claims in Independent Form Triggers Estoppel

November 26, 2003

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Last Month at the Federal Circuit - December 2003

Judges: Mayer (author), Clevenger, and

In Ranbaxy Pharmaceuticals, Inc. v. Apotex, Inc., No. 02-1429 (Fed. Cir. Nov. 26, 2003), the Federal Circuit affirmed a district court's denial of a preliminary injunction against Ranbaxy Pharmaceuticals, Inc. ("Ranbaxy").

Apotex, Inc. ("Apotex") and Ranbaxy are generic drug manufacturers, who both seek to market amorphous cefuroxime axetil, a broadspectrum antibiotic. Apotex is the owner of U.S. Patent No. 5,847,118 ("the '118 patent"), which is directed to a process for preparing amorphous cefuroxime axetil. Ranbaxy sought a DJ that it does not infringe the claims of the '118 patent. Apotex counterclaimed and moved for a preliminary injunction, arguing that Ranbaxy was infringing the claims of the '118 patent under the DOE. Apotex conceded that there was no literal infringement. Thus, the sole issue before the district court when making its decision on the preliminary injunction motion was Apotex's likelihood of success on its DOE theory. The district court concluded that prosecution history estoppel precluded Apotex's reliance on the DOE.

Apotex's original independent claim was for a process of making amorphous cefuroxime axetil using "a highly polar organic solvent," which dependent claims further limited to sulfoxide, formic acid, or an amide. During prosecution, the independent claim was rejected under 35 U.S.C. § 112, ¶ 2, the Examiner asserting that the term "highly polar organic solvent" was indefinite. Additionally, the independent claim was rejected under 35 U.S.C. § 103(a) as obvious over a prior art process of making the drug using acetone, which the Examiner assumed was a highly polar organic solvent. The dependent claims specifying particular solvents were objected to and indicated as being allowable if rewritten in independent form. In response, Apotex canceled the pending claims and replaced them with all new claims; the only independent claim presented ultimately became claim 1 of the '118 patent and was limited to the particular solvents recited in the previously objected-to dependent claims.

Ranbaxy's alleged infringing process uses acetic acid rather than the specifically recited solvents, and so Apotex moved for a preliminary injunction alleging infringement under the DOE. The district court found that prosecution history estoppel precluded Apotex's reliance on the DOE because: (1) Apotex had submitted a narrowing amendment for reasons related to patentability, and (2) Apotex had surrendered solvents of the same polarity as acetone, namely, acetic acid.

On appeal, the Federal Circuit addressed the issue of whether rewriting a dependent claim in independent form triggers prosecution history estoppel by first distinguishing its Bose Corp. v. JBL, Inc., 274 F.3d 1354 (Fed. Cir. 2001), decision. The Court observed that Bose had held that rewriting a claim to explicitly recite a previously inherent feature did not trigger estoppel, but that it had not addressed the issue of rewriting a dependent claim in independent form. The Federal Circuit stated that the correct focus for determining whether a narrowing amendment has been made is on whether subject matter that was originally claimed was surrendered for reasons related to patentability. The Court found that rewriting the dependent claims that recited specific highly polar organic solvents in independent form further defined and circumscribed the existing limitation of "highly polar organic solvent" for the purpose of putting the claims in condition for allowance.

In addressing whether Apotex could overcome the presumption of surrender, the Federal Circuit rejected Apotex's argument that it could not have foreseen that reciting particular solvents would constitute a surrender of an obvious structural equivalent of those solvents, particularly in light of Apotex's arguments that acetic acid was a known equivalent. However, the Federal Circuit observed that, before the district court, there was a dispute among the experts on the issue of the proper method of determining polarity. As such, the Federal Circuit noted that Apotex may be able to present sufficient evidence to rebut the presumption of surrender, and if so, the trier of fact must determine the proper method of determining polarity and whether acetic acid and acetone have the same polarity.