A blood-thinning drug has been given the go-ahead for use on the state-run National Health Service here in a move that is expected to revolutionise stroke prevention, it was announced Thursday. The drug - the first anti-clotting agent to be developed in almost 60 years - could eventually replace warfarin, the most commonly used therapy, which is based on rat poison, the British health authorities said. Almost a million patients suffering an irregular heartbeat could be eligible to take the new drug, called Pradaxa, which could prevent an additional 5,000 strokes a year. Warfarin is used by more than 500,000 patients in the UK. Users need close monitoring and regular blood tests to prevent potential excessive bleeding from cuts or stomach ulcers. Warfarin can also interact badly with other drugs and some foods including green vegetables and grapefruit, while alcohol can affect its action. Pradaxa, also known as dabigatran, works as well as warfarin, while a higher daily dose, of 300mg a day, is almost one-third more effective at reducing the risk of stroke. Patients taking the capsules do not have to be constantly checked, can eat what they like, and it is much easier to use with other medicines. Pradaxa costs 2.50 pounds a day - vastly more than about one pound for a month\'s supply of warfarin - and patients have to take it for life. It is estimated that high-dose Pradaxa in up to 900,000 eligible patients - many of whom are at risk but currently untreated - could prevent an extra 5, 000 strokes a year, saving the health authorities up to 59 million pounds in the first year. The drug is one of a new generation of anti-clotting agents aimed at preventing strokes and other potentially fatal problems associated with heart conditions.