Despite its benefits, warfarin is awkward for patients because it requires them to take periodic blood tests to make sure the drug's anti-clot-forming effort is successful. (Clinical trials show patients can take a fixed dose of Exanta, thus avoiding the constant blood-testing.)

If the warfarin effect is too great, patients can suffer from internal bleeding or other bleeding, such as from the gums during brushing. If the impact is too little, patients remain vulnerable to clots. In addition, warfarin interacts with many drugs, herbal medications and foods that can exacerbate or depress the blood thinner's effect. Exanta has fewer interactions with other products.

AstraZeneca began marketing Exanta in Germany on June 21, having secured European Union regulatory approval in late 2003 for preventing blood clots in patients who had undergone elective hip or knee replacement surgeries. This is a narrow use of the drug, but it's also one for which liver problems would be less likely to arise because patients won't take the drug for a long time. The EU approval calls for the drug to be administered orally for 11 days.

However, the big market -- and big controversy -- will be in chronic uses, such as atrial fibrillation or the installation of a mechanical heart valve. These patients would have to take Exanta for the rest of their lives. AstraZeneca is seeking European Union approval for expanded applications of the drug.

AstraZeneca is seeking FDA approval for three uses: preventing blood clots in veins for patients undergoing knee replacement surgery; preventing stroke and other clot-induced complications of atrial fibrillation; and long-term prevention of blood clots in veins after a patient has gotten a standard blood clot treatment.

AstraZeneca, which submitted its FDA application in late December, is seeking approval based on tests involving more than 30,000 patients. Exanta clinical trial results have appeared in such prestigious publications as The New England Journal of Medicine and The Lancet as well as at major cardiology conferences.

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