New patient safety tool aimed at reducing harm from warfarin/Coumadin

2008-05-26T08:00:00-05:00

Some old news bears repeating. Patients who take the blood-thinner Coumadin (or warfarin, the generic version) must closely monitor their risk from either too large a dose that can cause life-threatening bleeding, or too low a dose that could open up the risk for blood clots.

More than 3.8 million Americans were taking warfarin to prevent blood clots in 2005, according to the Agency for Healthcare Research and Quality (AHRQ), the research arm of the U.S. Department of Health & Human Services. Two million new people are prescribed the blood thinner annually.

AHRQ has just released a patient safety booklet, Your Guide to Coumadin®/Warfarin Therapy, aimed at reducing illness or death that can result from errors in dosing, alcohol use, added illnesses, and changes in diet that affect the safety of the drug. For example, because warfarin prevents blood from clotting, it may take longer than usual to stop bleeding following an injury. Vitamin K, found in spinach, broccoli, tea and other common foods, can affect how warfarin works. Vitamin K-rich foods need not be avoided, but the intake level of this vitamin should stay level, according to public health sources.

Warfarin is prescribed for people with heart arrhythmias (irregular heartbeat), venous thrombosis (blood clots in the veins), mechanical or other artificial heart valves, pulmonary embolism (a blood clot that traveled to the lung), and some who have experienced a heart attack or stroke. It works by preventing blood clots from forming or growing larger in your blood and blood vessels.

Blood tests, particularly at the beginning of therapy, are used to monitor whether a patient is taking too much or too little warfarin. The tests measure prothrombin time, or how long it takes for blood to clot. Those tests and patient health evaluations should be ongoing for patients on warfarin, according to experts.

About 17 percent of the 177,504 emergency room visits by Americans 65 or older during 2004 and 2005 was due to adverse effects from warfarin, according to a Centers for Disease Control and Prevention (CDC) study published in the Annals of Internal Medicine.

"Warfarin is an effective drug, but it must be used with special care to avoid dangerous bleeding," said AHRQ Director Carolyn M. Clancy, MD, in a written statement. "Individuals respond differently to warfarin, so the dosage must be personalized to each patient, and it is necessary for patients and clinicians alike to be aware of the factors that make for safe use of the drug."

In August 2007, the FDA added a recommendation to the warfarin label that genetic testing be performed before initiating warfarin therapy. About one-third of people prescribed warfarin possess two genes (CYP2C9 and VKORC1) that put them at higher risk for bleeding, according to the FDA.

AHRQ’s patient safety booklet can be accessed online or request that a copy be mailed by calling (800) 358-9295 or sending an e-mail to AHRQPubs@ahrq.hhs.gov.

Other information resources:

Children and Coumadin -- University of Michigan Health System

Coumadin safe recipes -- Dr. Gourmet, aka Timothy S. Harlan, MD, an associate clinical professor of medicine at Tulane University School of Medicine in New Orleans, and a former chef.

How to stay safe on Coumadin -- Johns Hopkins Health Alerts

Important information to know when you are taking: Coumadin and Vitamin K – National Institutes of Health

Flesh and Stone

New patient safety tool aimed at reducing harm from warfarin/Coumadin