AstraZeneca has won US approval for its cholesterol-lowering drug Crestor to treat hardening of the arteries.

The Food and Drug Administration approval means that the drug, which already has sales of more than $2 billion a year, can be marketed more widely as a treatment to slow the progression of atherosclerosis, or clogging of the arteries.

This is an important step to help differentiate Crestor from other cholesterol-lowering competitors. It means Crestor, which is already widely prescribed for high risk patients in the US, is the first of the widely used statin family of cholesterol drugs to win approval to treat atherosclerosis.

Atherosclerosis occurs when there is a build up of fatty deposits, forming areas called plaques, in the artery wall. These can cause the arteries to narrow, restricting the flow of blood to vital organs. They can also rupture, triggering a sudden, complete blockage of blood flow. In the heart this can cause a heart attack and in the brain it can cause a stroke.

Britain's second-biggest drug company, AstraZeneca, is relying on Crestor to drive growth but it received a set back earlier this week when research was published that showed patients at risk of heart failure who took the drug, alongside standard drugs for the condition, were just as likely to die as those on standard therapy alone. Astra is also facing a generic challenge to key patents on the medicine.

The drug maker has been running a major programme of clinical trials to try to prove its superiority to other similar statin drugs and this FDA approval could give Crestor an edge over other potent cholesterol lowering drugs such as Lipitor from Pfizer and Vytorin sold by Schering-Plough Corp and Merck & Co.

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