BOSTON - A federal judge in Massachusetts on Dec. 11 certified a nationwide class of direct purchasers of Nexium on their antitrust claims contending that the manufacturer of the heartburn medication and generic drug manufacturers entered into reverse-payment agreements to keep generic versions of the medication out of the market (In re Nexium [Esomeprazole] Antitrust Litigation, No. 12-md-02409, D. Mass.; 2013 U.S. Dist. LEXIS 173353).