WASHINGTON, Aug 18 (Reuters) - Concordia Pharmaceuticals Inc and Par Pharmaceutical Inc have settled charges they unlawfully agreed not to compete in the sale of a generic version of Kapvay, a drug used to treat attention deficit hyperactivity disorder, the U.S. Federal Trade Commission said on Tuesday.

The FTC had alleged Concordia, a unit of Concordia Healthcare Corp, had agreed not to sell a generic version of the drug in exchange for a share of Par's revenues. Par is a subsidiary of Par Pharmaceutical Holdings Inc..

Concordia and Par were the only two firms permitted by U.S. regulators to sell a generic version of Kapvay. The settlement bars them from enforcing anticompetitive provisions of their agreement, including the profit-sharing provision, the FTC said.

(Reporting by Timothy Ahmann; Editing by Sandra Maler)