New Study Finds Better Way to Determine Dose of Blood-Thinner Coumadin, But Improved Method May Not Be Available for Years

Medical researchers may have found a better way to determine the proper dose of a popular blood-thinning drug, which is taken by an estimated four million people in the United States.

Coumadin (generic name: warfarin) is commonly prescribed to prevent the formation of blood clots that can cause deadly heart attacks and strokes. However, determining the right dosage of the drug can be difficult. Many physicians are forced to resort to a trial-and-error approach, giving a standard dose then increasing or decreasing that amount based on the individual patient.

Studies have found that trial and error has failed half the time, and the problem is, giving too much of Coumadin can cause uncontrolled bleeding, while too little of a dose can allow deadly blood clots to form.

For many years, people prescribed Coumadin have complained that their doses did not work for them and doctors have had no more effective way to improve the results.

Now, researchers may have discovered a new formula which relies on gene testing to determine the proper dose of Coumadin. However, it could take years for the new formula to be tested and become standard practice in prescribing the drug, researchers said.

Gene Variations are Targeted

Researchers from the National Institutes of Health and several international medical organizations focused their work on variations in two genes, which can indicate the effective dose of Coumadin. In the study, about 5,700 patients who were already on stable doses of the drug reached through the trial-and-error method were examined.

A gene test was administered to the patients and other factors, including the patients’ age and weight, also were considered. The results were that the new formula arrived at the proper dose of Coumadin in about one of every three patients and was more accurate and quicker than prescribing by trial and error, the researchers said.

The study did not include an analysis of serious side effects associated with the drug or how tobacco and alcohol use might figure into blood thinner dosing, according to the study. Coumadin use in pregnant women has also been linked to birth defects, another factor not examined by the study.

Larger Study in the Works

But before you run to your doctor’s office and ask for you Coumadin dose to be based on your genes, hold on. Based on the encouraging results of the preliminary study, federal health officials want to embark on a larger, longer study of Coumadin patients beginning in April 2009.

Not until that after study, which could take three years to complete, will the genetic-testing method of determining the proper dose of Coumadin be widely adopted, researchers said. Some clinics have begun using gene tests and other advanced methods to more accurately determine Coumadin dosing, but most agree that the process is not yet cost-effective for most patients.

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