The U.S. Court of Appeals for the Federal Circuit reversed the district court’s finding of infringement of claims "corrected" by certificate of correction (COC), while permitting plaintiffs to pursue infringement allegations under the original, uncorrected claims, holding the COC was invalid. Central Admixture Pharmacy Services Inc. et al. v. Advanced Cardiac Solutions PC et al., Case No. 06-1307 (Fed. Cir., Apr. 3, 2007) (Gajarsa, J.).

Prior to initiating the lawsuit, Central filed a request under 35 U.S.C. § 255 for a COC to replace all occurrences in the patent of the word "osmolarity" with "osmolality." Both of these words measure the concentration of a solution. The U.S. Patent and Trademark Office (USPTO) issued the certification after the complaint was filed. Based on the claims (as amended by the COC) the district court (on summary judgment) found Advanced Cardiac Solutions PC (ACS) liable for willful infringement. ACS appealed.

The Federal Circuit began its analysis by noting that in order to invalidate a COC, the challenger must prove under a clear and convincing standard both that the corrected claims are broader than the original claims (a question of law) and that the presence of the clerical or typographical error is not clearly evident to one of skill in the art (a question of fact). The Court further noted that if "an error makes its own correction known to one of skill in the art, those errors do not raise serious public notice problems." In the contrast, if the mistake resulted "in another word that is spelled correctly and reads logically in the context of the sentence," then the error cannot be remedied by using a COC. Doing so will only result in broadening the patent claims.

In this case, the substitution of the corrected unit "osmolality" led to a slight deduction of concentration of the patented solution by 1 or 2 percent. Despite the mistake, the recited unit (osmolarity) still measures the appropriate property of the patented solution and the claimed range remains effective for the stated purpose in the specification. However slight the change of concentration was, there is a possibility for defendants’ accused solution concentration to fall outside of the original, "uncorrected" claims but within the "corrected," broader claim. Thus, by mistakenly using the word "osmolarity," Central made precisely the latter type of mistake that is incurable by a COC. As the Federal Circuit explained, to one of skill in the art, the concentration represents by osmolarity "is not a manifestly erroneous one."

Practice Note: In the process of prosecuting patents, the patentee should be very careful to choose clear and precise technical units or terms in the patent claims.

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