Anglo-Swedish drugmaker AstraZeneca has filed a lawsuit in the US District Court in New Jersey against Israel’s Teva Pharmaceutical Industries for infringing the patents protecting its heartburn drug, Nexium.

AstraZeneca initiated proceedings after Ivax Pharmaceuticals, which was bought by Teva earlier this year for $7.4 billion, filed an application to sell a copycat version of the drug in the US, although the first of Nexium’s (esomeprazole) five patents is not due to expire until 2014.

This follows a similar move by the company last month, when it sued Indian group Ranbaxy Laboratories for filing its generic version of Nexium in the USA. The drug is one of AstraZeneca’s most important growth products, with sales jumping 18% to $4.63 billion in 2005 and $3.13 billion of that coming from the USA, so the group will be doing everything it can to protect the agent’s exclusivity.

While now accepted as a fact of life for research-based pharmaceutical companies, this type of patent challenge has a particularly unwelcome resonance for AstraZeneca at present, coming soon after AstraZeneca lost a lawsuit aimed at defending its cardiovascular product Toprol XL (metoprolol) from generic competition in the USA.

But, in a statement, AstraZeneca stressed its full confidence in the patents, and said it will continue to vigorously defend and enforce its intellectual property rights protecting Nexium.