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Vitamin K Antagonists For DVT

Medically Reviewed by Melinda Ratini, DO, MS on May 03, 2022

If you’re being treated for a type of blood clot called a deep vein thrombosis (DVT), your doctor may have told you to watch your intake of things high in vitamin K, like spinach, kale, and even green tea. That’s because vitamin K helps your blood clot. Sudden changes in how much of these you eat or drink can interfere with a type of DVT medication called a vitamin K antagonist. These drugs hinder vitamin K’s clotting ability and reduce your chances of getting another DVT.

“Coumarin” is another name for this type of drug, one of several classes of medications doctors can use to treat DVT. The most widely prescribed coumarin (and the only one available in the U.S.) is warfarin (Coumadin, Jantoven). It was approved for human use back in 1954.

You might hear vitamin K antagonists called blood thinners, but they don’t really thin your blood.

Remember when you were a kid, and you got a cut that bled, then formed a scab? Our blood contains substances called clotting factors that stop bleeding and help this process. Vitamin K makes certain clotting factors. By blocking this action, vitamin K antagonists slow the clotting process. This helps keep clots that you have from getting larger and stop new ones from forming. They don’t stop clotting completely, but help blood flow through your veins more easily.

How Do I Take a Vitamin K Antagonist?

You take coumarins as a tablet by mouth once a day, just like a vitamin. Warfarin comes in several shapes and sizes because many manufacturers make it. The tablets are color-coded by dosage, ranging from pink (1 milligram) to white (10 milligrams). All drugmakers follow the same color guidelines.

Your doctor may recommend that you take your coumarin at the same time each day. That’s because these drugs can wear off quickly.

If you forget a dose, take it within 8 hours of your usual time. If it’s been longer than 8 hours, just take your pill the next day. Never double your dose. You can take warfarin before or after a meal.

If you forget to take your pill for 2 or more days in a row, contact your doctor’s office. They may want to change the dosage.

As with any prescription medication, don’t stop taking warfarin without your doctor’s OK.

Most people with DVT take warfarin for at least 3 months. Depending on your circumstances, your doctor may want you to take it longer.

Do I Have to Have Blood Tests?

Some medications require you to have regular blood tests to see if the drugs are working for you. Warfarin is one of them.

The test you’ll take is called a prothrombin time test, or for short, a protime (PT) test. Its result is reported as the international normalized ratio (INR). Your INR value is important. If it’s too low, the medication won’t work as well to prevent blood clots. If it’s too high, you’re at a higher risk of bleeding.

That’s why you need to keep up with the testing schedule your health care team recommends. Coumarin doses can be easily adjusted.

When you start taking warfarin, your doctor will probably recommend frequent tests so they can work out the right dose for you. After a week or two, you may need tests less often. This depends on your medical history, your risk for getting another blood clot, and how well you respond to coumarins.

Is There Anything I Can Do to Help With the Test?

To make sure your test results are as accurate as possible, don’t miss a dose of your meds. It’s OK to eat foods rich in vitamin K, but try to consume about the same amount every day. Make sure your health care team knows about every other medicine you take. That includes vitamins, supplements, over-the-counter medicines, and prescription drugs.

Many people enjoy a glass of wine or other alcohol on occasion. But if you take warfarin, talk to your doctor about how much – or little – you should drink. Alcohol can interfere with your body’s ability to form clots and put you at risk for bleeding. If you have no other risk factors, you may have to limit how much alcohol you have, but the occasional drink might be OK.

What About Risks and Side Effects?

Every drug has potential risks and side effects. With coumarins, the major risks have to do with clotting or bleeding. Clotting, due to not taking enough warfarin, might lead to another DVT, for example. And bleeding, due to too much warfarin, could lead to potentially serious bleeding in your digestive tract or brain.

But excessive bleeding can happen in any part of your body. Let your doctor know if you’ve had a fall or been in an accident. Look out for bruising or bleeding from your gums, in your urine, in your stool, or in your vomit.

Clots give clues too. A serious headache could be a symptom of a clot or bleeding in your brain, so get medical help right away – especially if you also have weakness and confusion. Also seek immediate medical help if you have bleeding that won’t stop or you cough up blood.

How Can I Reduce These Risks?

For most people with DVT, the benefits of a vitamin K antagonist outweigh potential risks.

The most important way to reduce your odds of any problems is to follow your health care team’s advice. You can cut your odds of bleeding by doing things as simple as using a soft toothbrush and waxed floss. Shaving with an electric razor can be safer, too.

Let all your health care providers know that you’re taking a vitamin K antagonist. That includes your dentist, if you’re having dental work done. It’s especially important to speak up if you’re having any type of surgery. You may have to reduce your dosage or stop taking it for a few days, depending on the kind of procedure you’re having.

Show Sources

SOURCES:

Hematology, American Society Hematology Education Program: “Optimizing quality care for the oral vitamin K antagonists (VKAs).”

Cleveland Clinic: “Warfarin (Coumadin) Anticoagulant Medication.”

British Journal of Clinical Pharmacology: “Warfarin: almost 60 years old and still causing problems.”

American Heart Association: “A Patient’s Guide To Taking Warfarin.”

UpToDate: “Patient education: Deep vein thrombosis (DVT) (Beyond the Basics),” “Warfarin and other VKAs: Dosing and adverse effects.”

Health Navigator: “Warfarin and INR.”

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