Dr. Jacqueline Gerhart: Is warfarin safe?
Madison, Wisconsin - UW Health Family Medicine physician Jacqueline Gerhart writes a column that appears Tuesdays on madison.com and in the Wisconsin State Journal. Columns are re-published here with permission.
Dear Dr. Gerhart,
My sister was just put on warfarin (Coumadin) to thin her blood. Wasn't that originally used as rat poison? Is it safe?
The main reason to take warfarin is to decrease your risk of forming blood clots. People who have had blood clots in their legs or lungs are often put on warfarin. People with abnormal heart rhythms (like atrial fibrillation), heart valve replacements, strokes, or heart attacks may also need warfarin.
A bit of Wisconsin history: The medical benefits of warfarin were actually refined for medical use at UW-Madison. Near the UW Hospital, there is a building called the Wisconsin Alumni Research Foundation (WARF). Warfarin is named after this organization. Warfarin is known colloquially as a "blood thinner," but in reality, it doesn't thin the blood. The weight of the blood and its "thickness" stay the same, but its ability to form clots decreases. Essentially, it is an anti-clot or anticoagulation agent.
How warfarin was discovered: In the 1920s, there was an outbreak of cattle disease in the northern U.S in which cattle bled to death. It seemed that the dead cattle had ingested spoiled sweet-clover-based feed. A cattle farmer named Deer Park took one of his dead heifers, some of his spoiled clover hay, and a milk can full of blood that wouldn't coagulate, and showed up at the UW School of Agriculture. Scientist Karl Link set out to isolate the hemorrhagic agent in the spoiled hay. It took his lab workers over 5 years to recover 6 mg of the substance from the sweet clover that caused bleeding. This substance, which interacts with vitamin K in the blood, was named warfarin. It was first registered for use as rat poison in 1948. It was then studied in humans, and was approved for medical use to help prevent blood clots in 1954.
Warfarin is usually safe when well-monitored. This requires collaboration between the patient, the pharmacist, the laboratory, and all of the patient's health care providers. We monitor warfarin's affects on your blood with a blood test called an INR. For those not on warfarin, a normal INR is around 1. For those put on warfarin for atrial fibrillation or a clotting disorder, their INR should usually be between 2 and 3. For those on warfarin for a mechanical heart valve, the INR should usually be is between 2.5 and 3.5. In patients on warfarin, a high INR poses a risk for bleeding while a low INR increases their risk for clots.
People on warfarin, should be aware of the many interactions warfarin has with foods and medications. Grapefruit juice, green leafy vegetables (that are high in vitamin K), certain antibiotics and other anticoagulants like aspirin affect warfarin. Check with your doctor or pharmacist before changing or starting any medications or making any major dietary changes. Call the clinic if you miss a dose, or are out of medication. Also, monitor yourself for bruising, leg or calf pain, or shortness of breath.
As with all medications, discuss the risks and benefits for your specific case with your doctor. There are situations (such as patients at risk of falls or with bleeding ulcers) where the risk of bleeding on warfarin outweighs the benefits.
This column provides general health information and is not specific advice intended for any particular individual(s). It is not a professional medical opinion or a diagnosis. Always consult your personal health care provider about your concerns. No ongoing relationship of any sort (including but not limited to any form of professional relationship) is implied or offered by Dr. Gerhart to people submitting questions.
Date Published: 01/10/2012