BILLIONS were wiped off the shares in two pharmaceutical companies yesterday after a US safety official voiced concerns about two best-selling drugs.

David Graham, of the US Food and Drugs Administration (FDA) told the Senate Finance Committee that a closer review of AstraZeneca's anti-cholesterol drug Crestor was needed following fears it caused acute kidney failure.

Astra shares fell seven per cent while GlaxoSmithKline dipped four per cent after Mr Graham said its Serevent treatment for asthma should be looked at for increased risk of death among patients.

Both companies rejected the claims that their drugs were unsafe. In its response, Glaxo, which employs more than 1,000 people in Barnard Castle, County Durham, said it stood firmly behind Serevent, which was safe and effective when used appropriately and in accordance with labelling and treatment guidelines.

Serevent was introduced in the US in 1994 after four years on the market in the UK and has been prescribed to millions of patients.

Last year, the FDA put a black box warning on Serevent to state the potentially higher risk of mortality, but said the benefits of the drug outweighed the risks.

Sales of Serevent totalled £433m last year and its key ingredient is also used in its best-selling respiratory drug, Advair.

Dr Graham, who is associate director for science in the FDA's Office of Drug Safety, also said regulators should look again at three other treatments by drugmakers Roche, Pfizer and Abbott Laboratories.

His comments come at a difficult time for the drugs industry, after US manufacturer Merck was forced to withdraw its Vioxx arthritis drug when it was linked to heart problems.

Investor confidence in AstraZeneca was also shaken by the provisional rejection of its blood-thinning drug Exanta by US regulators in September amid concerns that it could cause liver failure.