(Adds details of legal challenge, background)
April 28 Actavis Plc said on Monday it has sued the U.S. Food and Drug Administration, challenging its decision to award exclusive rights to Teva Pharmaceutical Industries Ltd to sell a generic version of Pfizer Inc's blockbuster painkiller Celebrex.
A similar lawsuit was announced Friday by Mylan Inc over generic drug marketing exclusivity for Celebrex.
Actavis alleges that FDA improperly awarded sole exclusivity to Teva despite an earlier ruling from the U.S. Court of Appeals for the Federal Circuit that resulted in the expiration of that entitlement.
Teva, the world's largest generic drugmaker, earlier this month signed a deal that would allow it to launch a generic version of Celebrex in December. Celebrex's basic chemical patent is set to expire this May.
Deals between patent holders and generic drugmakers have come under increased regulatory scrutiny because of their potential to delay the launch of cheaper medicines.
Celebrex, which is used to treat arthritis pain and inflammation, generated about $2.92 billion in sales in 2013, according to Pfizer's annual regulatory filing. (Reporting by Susan Kelly in Chicago; Editing by Bernard Orr and Richard Chang)