What began as a patent litigation case spurred an antitrust case and ended with the Fourth Circuit’s latest reversal of class certification in In re Zetia (Ezetimibe) Antitrust Litigation Luckily, no expertise in pharmaceutical patent litigation or antitrust law is required to break down the court’s clarification of Federal Rule of Civil Procedure 23’s numerosity requirement. In short, Merck developed a cholesterol-lowering drug that it patented and marketed under the name Zetia, with its patent giving Merck the exclusive right to develop the drug through April 2017. In 2006, another pharmaceutical company, Glenmark, sought FDA approval to market a generic version of Zetia on the basis that Merck’s patent was invalid. Merck promptly sued Glenmark for patent infringement, and the two companies eventually settled the case with an agreement that Glenmark could launch its generic version of the drug in December 2016. Alleging violations of federal antitrust law, the plaintiffs in the present case sued both Merck and Glenmark on behalf of a putative class that included drug wholesalers who purchased Zetia directly from Merck.