FDA Stresses Test for Blood-Thinning Drug Warfarin

In a press release, The U.S. Food and Drug Administration has announced new and important information in regard to a commonly prescribed drug for blood-thinning, warfarin (coumadin).

Warfarin, the generic form of coumadin, is the second most common drug - after insulin -implicated in emergency room visits for adverse drug events.

According to the FDA, 2 million persons start taking warfarin (coumadin) in the United States every year to prevent blood clots, heart attacks and stroke. However, taking this drug is tricky because the exact dose of it should be taken to get full benefits and limit risks. People taking a dose lower than needed may be at risk of developing dangerous blood clots. A person who gets an overdose may be at risk of life-threatening bleeding.

The proper dosage of warfarin (coumarin) depends on many factors: age, gender, body weight, diet, usage of other medications, and genetic makeup.

The presence of certain genes may affect how warfarin (coumadin) is metabolized. So there is a need for proper genetic testing for determining the proper dose of this drug that a patient need. The FDA is warning about the use of genetic testing for the correct determination of dosage level for people needing to take coumarin (warfarin).

Until now, the initial and continue dosage for coumarin (warfarin) was based on a simple blood test called PT (Prothrombine Time). In this test a blood sample is extracted from the patient and the time needed for this blood to coagulate is measured in seconds. Then, this PT is compared to the expected value in healthy people, known as the International Normalized Ratio or INR.

However, now, the FDA is warning doctors and health care providers to use a genetic test to better estimate the dosage needed for any people who is need of coumarin. This genetic test for genes CYP2C9 and VKORC1 which research have shown that are present in people who metabolize coumarin in a different metabolic pathway way and prevent coumarin to have a full effect. About 30% of US people metabolize warfarin in this different metabolic path. Thus, the need of the test for a better estimation of warfarin (coumarin) dose.

The determination of medications and its usage based on genetics in the most new trend in medicine and pharmaceutics known as pharmacogenetics or pharmacogenomis. In this new area of the medical practice drugs are to me delivered to patients according to their genetic make up. It is a personalized medication scheme targeted to the specific patient.

The FDA's Critical Path Initiative funded a research project with the University of Utah and the Critical Path Institute of Tucson, Ariz., to develop genetically based instructions for warfarin dosing.

Source: FDA Approves Updated Warfarin (Coumadin) Prescribing Information. FDA Press Release.

URL: http://www.fda.gov/bbs/topics/NEWS/2007/NEW01684.html