AstraZeneca is facing generic competition to its high blood pressure drug Toprol XL (metoprolol succinate) in the USA, after a court ruled that key patents covering the product were invalid.

AstraZeneca has said it will appeal the decision, which all but clears the way for generic copies of the $1.3 billion product from Novartis’ Eon Labs subsidiary, KV Pharmaceuticals and Andrx Corp, although these still need to be approved by the US Food and Drug Administration.

The Anglo-Swedish drugmaker insists that its patent protection on Toprol XL should remain valid until September 2007. The product is sold outside the USA as Seloken-ZOK.

Analysts said copycat versions could be on the market within the next few weeks, assuming the FDA moves swiftly to approve the copycat versions, and would likely lead to a steep decline in Toprol XL US sales.

This is the latest in a series of setbacks at AstraZeneca, and affects a product which is currently its fourth largest brand and accounts for around 5% of total group sales. A hole was knocked in the firm’s near-term product pipeline after antithrombotic drug Exanta (ximelegatran) was rejected by the FDA towards the end of 2004, while more recently two candidate drugs, for heart arrhythmia and incontinence, have been terminated on poor clinical trial results.

Meanwhile, two of AstraZeneca’s other top products with combined sales of around $6 billion in 2004 – the gastrointestinal drug Nexium (esomeprazole) and Seroquel (quetiapine fumarate) for schizophrenia – are also facing challenges by generic manufacturers.

This has lent real urgency to efforts aimed at building the company’s product pipeline, and AstraZeneca has signed a string of new licensing deals in recent weeks, including a deal valued at up to $1 billion with Atherogenics for AG-1067, a treatment for atherosclerosis.

In December, AstraZeneca also offered to buy cancer drug development company KuDOS Pharmaceuticals for $210 million, and signed a $300 million licensing deal with US company TargaCept for a series of compounds in development for diseases of the central nervous system.