Joint brief of the United States and the Federal Trade Commission, as amici curiae before the United States Court of Appeals for the Second Circuit, in support of plaintiffs-appellants, who were direct purchasers of the prescription brand-name drug DDAVP. Plaintiffs had brought this putative class action under Section 4 of the Clayton Act, 15 U.S.C. § 15, alleging that defendants Ferring B.V. and Ferring Pharmaceuticals, Inc., who owned the patent for desmopressin acetate -- the active ingredient in DDAVP, and Aventis Pharmaceuticals, Inc., the patent's exclusive licensee in the United States, violated Section 2 of the Sherman Act, 15 U.S.C. § 2, by maintaining and enforcing a patent procured by intentional fraud on the Patent and Trademark Office (PTO). In their brief, the antitrust agencies urge the court of appeals to reverse the district court's holding that plaintiffs lacked antitrust standing to bring monopolization claims against defendant drug manufacturers arising out of the manufacturers' maintenance and enforcement of a patent allegedly procured through intentional fraud on the PTO (a so-called "Walker Process" antitrust claim).