Impax Laboratories Inc. said it will pay a royalty to settle a dispute related to the new formulation of Endo International plc's extended release opioid painkiller Opana.

The companies will modify an existing agreement so Endo International receives a royalty on the sale of Impax's generic version of the drug, starting Jan. 1, 2018.

The royalty is subject to elimination based on certain commercial conditions.

Impax had sought U.S. Food and Drug Administration approval in 2010 to sell a generic version of the original Opana, resulting in litigation from Endo International and its unit Penwest Pharmaceuticals.

The parties had settled the dispute that same year, granting Impax a nonexclusive license to the drug plus any future patents. Opana's patents can be extended until November 2029.

The new Opana ER formula and Impax's generic version had combined total net sales of $229 million for the year ending March 31.