Gene Testing Recommended Before Prescribing Warfarin

Warfarin, a widely used but potentially dangerous drug, should not be prescribed without first determining the patient's genetic profile.

Bleeding complications from warfarin are responsible for about 30,000 emergency room visits a year in the United States. Hemorrhaging, as a result of taking warfarin, can even be fatal. Studies have shown that the risk of a serious bleeding episode into the brain or intestine, for example–is highest soon after treatment has begun.

Variations in the activity of two genes can greatly increase the potency of warfarin, a pill that slows coagulation of the blood—about 2 million Americans start taking it each year. Many continue to take the drug for the rest of their lives. One of the genes involved, CYP2C9, has a role in metabolizing the drug. The other, VKORC1, determines a person's sensitivity to the drug's blood-thinning action. The gene profile accounts for about 40% of a person's response to the drug, the other variables being age, sex, diet, and overall health.

The US Food and Drug Administration (FDA; Silver Spring, MD, USA) officials, for the first time, provided data on the usefulness of gene tests in the "label," or official instructions, of any popular drug.
Lawrence J. Lesko, of the agency's Center for Drug Evaluation and Research, said, "It shows that genomic medicine has moved into the mainstream."

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US Food and Drug Administration