Anglo-Swedish drugmaker AstraZeneca says that the US Food and Drug Administration has approved a new indication for the prescription proton pump inhibitor Nexium for the treatment of Zollinger-Ellison syndrome, a rare but serious chronic condition characterised by development of tumours that secrete excessive levels of gastrin, a hormone that stimulates the stomach to produce acid.

Nexium (esomeprazole) is already indicated for the treatment of gastroesophageal reflux disease in adults and children aged 12 to 17 years, and to reduce the risk of non-steroidal anti-inflammatory-associated gastric ulcers in at-risk patients.

The new approval is based on clinical data in which 21 patients received one of several doses of the agent, depending on their symptoms and the degree of their acid output. The 12-month, open-label trial demonstrated that Nexium effectively maintains basal acid output control in this patient population.

Sales of Nexium in the first half of 2006 came in at $2.47 billion, a 9% increase year-on-year. The product is AstraZeneca's top seller, but is facing a challenge from Teva which is seeking approval for a generic version of the drug, although AstraZeneca insists it will not use patent protection in the USA until 2014.