In a move widely anticipated by industry observers, UK drug giant AstraZeneca is dragging Indian generics maker Ranbaxy Laboratories to court in the USA to block the sale of a copycat version of its blockbuster antiulcerant Nexium (esomeprazole magnesium) while the drug’s patents are still in force.

The lawsuit follows Ranbaxy’s Abbreviated New Drug Application filed with the US Food and Drug Administration last month detailing its intent to market a generic formulation of Nexium before the product loses its protective armour - comprised of six patents set to expire from 2014 through 2019.

Marking yet another aggressive gamble by the Indian firm, Ranbaxy's challenge, if successful, would allow it to sell a copycat version of Nexium as early as October 2007. But AstraZeneca says it has “full confidence in and will continue vigorously to defend and enforce its intellectual property rights protecting Nexium.” And the UK group, Europe’s third biggest pharmaceutical firm, will certainly be throwing everything it has into the battle - Nexium is its top-selling drug, with sales already at $2.3 billion in the first half of 2005.

This is the second recent challenge to one of AstraZeneca's biggest-selling products: 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).