The generic threat to AstraZeneca’s antiulcerant blockbuster Nexium has moved on a stage with the news that Ranbaxy’s copycat version of the drug has received tentative approval from regulators in the USA.

The Indian drugmaker’s US subsidiary says that the Food and Drug Administration has given a provisional go-ahead to manufacture and market generic Nexium (esomeprazole) 20mg and 40mg delayed-released capsules. Ranbaxy said it has first-to-file status on the drug, providing it with 180 days of marketing exclusivity.

This, Ranbaxy said, offers “a significant opportunity in the future”, especially as Nexium is the second-largest selling drug in the USA with annual sales of around $5.5 billion. The treatment is currently approved for erosive oesophagitis, heartburn and other symptoms associated with gastro-oesophageal reflux disease.

The Anglo-Swedish firm sent a statement to PharmaTimes World News saying that it “continues to have confidence in its Nexium patents and will vigorously defend its intellectual property”. AstraZeneca is currently embroiled in patent litigation over Nexium with Ranbaxy, its fellow Indian firm Dr Reddy’s and Israel’s Teva Pharmaceutical Industries which are also planning to sell a copy of the drug, which has patent protection that is due to expire starting 2014 through to 2019.

The loss to earnings if generic versions of Nexium appear before then would be disastrous for AstraZeneca but any approvals are a long way off. Ranbaxy still requires final approval from the FDA before it can consider launching generic esomeprazole and that could take a couple of years.