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A new study of the blood-thinning drug warfarin has found the majority of heart patients receiving it had the wrong clotting levels, leading to an increased death rate.
The drug is given to many patients with an abnormal heart rhythm, who are at risk of a blood clot which could cause a stroke. It reduces their stroke risk by 60 per cent.
But the international study by researchers including Professor Harvey White, of Auckland City Hospital, found that two-thirds of the more than 3000 patients had blood-clotting levels outside the desired range 75 per cent of the time.
Those with poor control of their blood's consistency had an annual death rate of 4.2 per cent, compared with 1.7 per cent among those whose control was good.
The poor-control group also fared worse in rates of heart attack, stroke, major bleeding and blood clots, says the research report, published in an American journal, the Archives of Internal Medicine.
Professor White said yesterday warfarin was an important but dangerous drug and many people could not take it.
Clotting levels in patients taking warfarin could be affected by other medicines, by eating foods including broccoli, and by individual variability.
"In some patients [clotting levels are] all over the place the whole time."
In the community, he said, results were much worse than in the trial.
Around 60,000 patients had unstable heart rhythm in New Zealand, but only half were prescribed warfarin. For the rest, the benefits did not warrant its risks.
Warfarin's limitations have prompted calls for newer anti-clotting drugs.
Professor White is involved in a study of such a drug, called rivaroxiban. He said that, unlike warfarin, it did not necessitate ongoing blood tests and it did not have warfarin's interaction problems.
"It looks very promising, but we would need to prove that," Professor White said.
Warfarin
* Warfarin is a blood-thinning drug used to protect against strokes
* It is used by about 30,000 New Zealanders
* Researchers say it does not work effectively
* Warfarin is also used as a rat poison
