Ranbaxy has received tentative approval from the U.S. Food and Drug Administration for a generic version of AstraZeneca's Nexium.

Ranbaxy has received tentative approval from the U.S. Food and Drug Administration for a generic version of AstraZeneca's Nexium. Nexium, whose active ingredient, esomeprazole magnesium, is packaged in delayed-release capsules, is used to treat gastroesophageal reflux disease (acid reflux) and heartburn, Ranbaxy said in a statement Thursday. The company, based in Gurgaon, in Haryana state, has first-to-file status on the drug under the Hatch-Waxman Act of 1984, designed to promote generic versions of patented drugs, giving Ranbaxy a potential 180 days of exclusive marketing when the patent on Nexium expires. An automatic 30-month legal stay on generic versions of the drug will be lifted on April 14.

AstraZeneca has said it has patents that are legally valid from 2009 to 2019. Ranbaxy could launch in April once it gets final approval from the FDA but risks a legal challenge from AstraZeneca. Company officials declined comment on when they plan to take the drug to the U.S. market.

Ranbaxy has received approval to manufacture both 20-milligram and 40-milligram capsules. It said Nexium is the second-largest-selling drug in the United States, with total annual market sales of $5.5 billion.

AstraZeneca’s patents for Nexium, which is distributed in around 100 countries, have also been under threat in Europe. In November, the European Patent Office upheld a patent for the formulation of Nexium in a slightly amended form. In June 2005, the patent had been challenged by Germany’s Ratiopharm and Hexal, a unit of Novartis , Slovenia-based Krka; and Israel’s Teva Pharmaceutical.

Ranbaxy made 28 filings for generic drugs in its largest market, the United States, last year and received 18 approvals. It estimated it has first-to-file status on 18 products, which the company, according to a Jan. 17 press release detailing its 2007 results, valued in total at $27 billion.