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Warfarin: 12 Things You Didn't Know About This Blood Thinner

Medically reviewed on Jan 15, 2018 by L. Anderson, PharmD.

Warfarin: A Safe Generic?

The year was 1954. Coumadin, a widely used blood-thinner (anticoagulant), was approved to help prevent potentially deadly blood clots. Warfarin, the more affordable generic form, became available years later, but concerns arose about the safety of switching between the brand and generic. Some patients, and even doctors, were afraid to switch. However, studies have shown there are few, if any, risks of using generic warfarin.

Your doctor may schedule more frequent monitoring when first switched to monitor your individual response. Small dose adjustments may be needed until blood levels remain in the target range. Today, most patients use the generic warfarin from the outset; however, the brand product Coumadin is still available if you choose. Another affordable generic warfarin called Jantoven is also in pharmacies.

Color-Coded for Safety

Warfarin is considered a high-alert drug by the Institute for Safe Medication Practices. Generic warfarin tablets may come in different shapes, but each strength comes in just one color. For example, the 5 milligram (mg) tablet, one of the most common strengths, comes in a peach/light orange color. It's always a peach/light orange color, no matter the manufacturer. This is not the case with most other medications. Before you leave the pharmacy, make sure the color of your tablets match the strength your doctor prescribed. If you have questions, speak directly with the pharmacist. Taking the wrong dose may lead to dangerous clots or excessive bleeding. You can also use the Pill Identifier Wizard to verify medications.

Vitamin, Herbals and Natural Supplements

Warfarin drug interactions deserve your attention. For example, St. John's Wort, sometimes used to help with mild depression, reduces the effectiveness of warfarin by boosting production of enzymes that break down warfarin. Other supplements you should avoid that may interact with warfarin include:

Food and Drinks Can Interact, Too

Most people who take warfarin are aware that eating green, leafy vegetables like spinach, kale, or turnip greens may affect the blood thinning ability of warfarin. These foods contain vitamin K that can block warfarin action. However, did you know that other foods or beverages may affect the therapeutic action of your warfarin, too?

In general, diets should remain consistent while taking warfarin.

Bleeding Risk Precautions

While on warfarin, you might bleed more easily, so it's important to take precautions. For example, use a soft toothbrush, waxed dental floss, and an electric razor to avoid accidental cuts. Avoid sharp objects and be wary of falling risks, like climbing a ladder.

Many prescription drugs interact with warfarin; have your pharmacist check for all interactions. Even over-the-counter (OTC) drugs such as aspirin, NSAIDs like ibuprofen (Morin, Advil) or naproxen (Aleve), and cimetidine (Tagamet) may have an effect. It's worth your time to have a drug interaction screen run with each new prescription, OTC or herbal/vitamin supplement.

Vitamin K to the Rescue

No doubt many patients are nervous about taking a blood thinner. However, one advantage of using warfarin, as opposed to newer next generation anticoagulants, is that bleeding events can be reversed with the use of Vitamin K. In fact, it's the vitamin K you were told to be wary of in green, leafy vegetables - but in medication form.

However, Praxbind (idarucizumab), a bleeding reversal agent for the newer oral anticoagulant Pradaxa, was approved in October 2015.

And what if you have a serious bleeding episode while on a blood-thinning medication? Should you stop it all together? A 2016 observational study published in Stroke suggests no -- that most people will benefit from restarting their blood thinning medication to help prevent clots and lower the risk of stroke and heart attacks. The researchers also found that Pradaxa (dabigatran) may be less likely than warfarin to cause recurrent bleeding. Plus, there's also Praxbind as a reversal agent. Ultimately, your doctor will help guide you to the best agent for your needs.

Not a Friend to Rodents

Warfarin may be a life-saving drug for you, but it's a killer for rats. In fact, warfarin was the first anticoagulant "rodenticide". Rodenticides are pesticides that kill rodents. Warfarin was used widely as a rodenticide, but today it's use is declining as many rodents have grown resistant to it.

Rodents include not only rats and mice, but also squirrels, woodchucks, chipmunks, porcupines, nutria, and beavers. As in humans, warfarin use stops normal blood clotting in rodents. Although rodents play important roles in nature, they can carry disease and may sometimes require control.

Birds of Prey Getting a Full Warfarin Dose, Too

Killing rats and other rodents with warfarin rodent poison led to a problem, the death of birds of prey, like owls and hawks, who eat rodents who have ingested the poison. In fact, North American lawmakers moved to restrict the use of rodent poisons based on blood thinners, as studies show that the toxins accumulate in birds of prey and other animals.

Another problem? Rodent traps containing poison left outside can be consumed by other animals - and in the worse case scenario - a child might get their hands on it.

Painful Purple Toes

Purple Toe Syndrome may sound like a by-product of wearing high-heels, but it's actually a fairly rare complication associated with early warfarin use, usually within the first 3 to 8 weeks of treatment. This condition is thought to be due to small emboli in the blood vessels which cause a purple color in the toes and feet. Other symptoms include a cold feeling in the feet, pain, and possible sloughing off of the skin (necrosis).

Typically warfarin therapy is stopped with this diagnosis and another type of anticoagulant is used. Check with your doctor immediately if these symptoms appear.

(Not So) Happy Hour

Warfarin is notorious for it's drug interactions, and that includes alcoholic beverages. Excessive use of large amounts of alcohol is known to affect how warfarin breaks down in your body (metabolism) and can increase the risk of bleeding. Alternatively, in patients with liver disease (cirrhosis) who abuse alcohol chronically, the risk for clotting may increase.

The bottom line? In general, avoid large amounts of alcohol. Moderate consumption (1-2 drinks per day) are not likely to affect the response to the anticoagulant in patients with normal liver function, but always check with your doctor for a recommedation specific for you.

Is Your Blood Really Thin?

Warfarin is often referred to as a "blood thinner," but this is a misnomer because warfarin (and other coagulation modifiers) do not actually "thin" the blood.

For example, when you cut yourself, there is a series of clotting factors found in your blood that help to form a clot to stop the bleeding. Warfarin actually blocks (inhibits) these vitamin K-dependent clotting factors and other proteins to keep the blood anti-coagulated ("thin"). That's also why vitamin K can be given to stop excessive bleeding when it occurs during warfarin treatment.

Cost-Saving Generic

Many patients are being switched from warfarin to a new generation of anticoagulants that protect well against blood clots, but can be very expensive.

For some patients, their insurance will pay for the more expensive drug, and - a big plus - no regular blood tests are required with these new agents. But for patients who have limited or no insurance, these expensive drugs can be a hardship.

Generic warfarin runs only $4.00 for a month's supply at many retail pharmacies, but if you have to pay for the blood tests, too, that could add up quickly. Talk to your doctor about the best option if you require a life-saving blood thinner, say for atrial fibrillation or a deep vein thrombosis (DVT).

Finished: Warfarin: 12 Things You Didn't Know About This Blood Thinner

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Further information

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