Anglo-Swedish drug maker AstraZeneca PLC said Tuesday that Indian drug maker Ranbaxy Laboratories Ltd. has applied to manufacture a copy of its top-selling drug Nexium, which is used for treating persistent heartburn caused by acid reflux disease.

AstraZeneca said Ranbaxy submitted an Abbreviated New Drug Application with the U.S. Food and Drug Administration for the 20 milligram and 40 milligram versions of Nexium, challenging patents that are due to expire in 2018.