Cubist Pharmaceuticals, Inc. v. Hospira, [2015-1197, 2015-1204, 2015-1259] (November 12, 2015), the Federal Circuit approved the use of a Certificate of Correction to correct information not available at the time the application was filed.

At the time the application was filed, and until well after that patent was issued, it was universally believed that the asparagine amino acid in daptomycin was the L-isomer of asparagine, as set forth in the structural diagram in the patent.  Years after the issuance of the patent researchers discovered that daptomycin actually contains the D-isomer of asparagine, not the L-isomer. Cubist sought to correct the error by requesting a certificate of correction from the Patent and Trademark Office (“PTO”) pursuant to 35 U.S.C. § 255, which was granted.

In subsequent infringement litigation with Cubist, Hospira argued that the PTO had erred by issuing the certificate of correction because the change in the structural diagram altered the substance of the claims, broadening their reach.  However, Cubist’s expert testified that the specification made it clear that the claims of the patent were directed to daptomycin, not to the variant containing the L-isomer of asparagine. Because it was plain that the claims were directed to daptomycin, it was appropriate for the PTO to correct the error in the structural diagram.

The Federal Circuit said that once the PTO has issued a certificate of correction, a
court may invalidate the certificate only upon a showing of clear and convincing evidence that it was improperly issued, which Hospira failed to do.  The Federal Circuit said that the problem with Hospira’s argument was that the district court did not view the change in the diagram as changing the scope of the claims at all. Instead, the district court regarded the change as simply conforming the structural diagram to the compound described in the specification and covered by the claims.