Anglo-Swedish pharmaceutical giant AstraZeneca has been hit by a challenge to its big-selling gastrointestinal drug Nexium (esomeprazole) in the USA.

Indian drugmaker Ranbaxy Laboratories triggered the challenge by filing for approval to market 20mg and 40mg delayed-release capsule formulations of Nexium, which is approved in the USA for the treatment of gastro-oesophageal reflux disease and gastric and duodenal ulcers.

AstraZeneca now has 45 days to file a case alleging patent infringement against the Indian firm, which would automatically bar the US Food and Drug Administration from approving the generics for 30 months, unless AstraZeneca loses its court case in the interim.

If successful, Ranbaxy’s challenge would allow it to market generic version of Nexium as early as October 2007. At issue are additional patents that provide patent protection on AstraZeneca’s product out to 2018.

This is the second challenge to one of AstraZeneca’s biggest-selling products in recent weeks. Towards the end of September, Israeli generics company Teva Pharmaceutical Industries filed for approval to market a copycat version of AstraZeneca’s schizophrenia drug Seroquel (quetiapine) [[29/09/05a]].

Nexium is AstraZeneca’s best-selling drug, with sales of $2.3 billion in the first half of 2005, while Seroquel racked up $1.3 billion [[29/07/05d]]. US sales of the two drugs were $1.5 billion and $933 million, respectively, in the same period.