Issue 165 | March 1, 2004
Infectious Estoppel: Federal Circuit Applies Prosecution History Estoppel to Unamended Claim

In Glaxo Wellcome v. Impax Labs., Inc., 2004 U.S. App. LEXIS 1324 (Fed. Cir., January 29, 2004) the Federal Circuit applied the principle of prosecution history estoppel to a claim that had not been subject to a narrowing amendment during prosecution.

Glaxo Wellcome sued Impax for infringement of U.S. patent 5,427,798, whose claims were directed to a composition comprising the antidepressant bupropion and hydroxypropyl methylcellulose ("HPMC") (a sustained release agent). The Impax composition employed hydroxypropyl cellulose ("HPC") rather than HPMC for sustained release. At issue was whether HPC was an equivalent of HPMC.

The application that matured into the '798 patent was filed with two types of claims, those that recited the HPMC limitation and those that did not. During prosecution the examiner rejected the claims not containing the HPMC limitation for lack of enablement. In response, the applicant amended these claims to include HPMC, thereby overcoming the rejection. After a Festo analysis, the court held that prosecution history estoppel prevented Glaxo from asserting that HPC in the accused Impax tablet was an equivalent of HPMC and, thus, held that the Impax composition did not infringe the claims that had been amended, affirming the lower court decision.

Glaxo argued, however, that prosecution history estoppel should not apply to claim 1 of the patent, which was filed with the HPMC limitation and not subject to narrowing amendments during prosecution. The court was not persuaded.

The court referred to Builders Concrete, Inc. v. Bremerton Concrete Prods. Co., 757 F.2d 255, 260 (Fed. Cir. 1985) for the proposition that subject matter surrendered via claim amendments during prosecution is also relinquished for other claims containing the same limitation. See also Allen Engineering Corp. v. Bartell Industries Inc., 299 F.3d 1336, 1350, 63 USPQ2d 1769, 1777 (Fed. Cir. 2002) ("Any argument-based estoppel affecting a limitation in one claim will also extend to all claims in which that limitation appears.").

In analyzing the Glaxo patent, the court noted that the HPMC limitation was determined to be critical for patentability and there was no evidence that the examiner considered this limitation any less critical to claim 1 as compared to the other claims. To use a broader interpretation of the HPMC term in claim 1 as compared to the other claims, the court stated, would create an inconsistency within the patent. The court stated that there must be "consistent interpretation of claim terms within a patent in view of the prosecution history," and "different claims of a single patent should not be afforded different ranges of equivalents for the same claim term, absent an unmistakable indication to the contrary."

Thus, prosecution history estoppel may apply even to unamended claims, further leveling whatever barriers might have existed to the use of estoppel to limit the doctrine of equivalents.

Michael S. Greenfield is a partner at the law firm of McDonnell Boehnen Hulbert & Berghoff.

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