Anticoagulation Services

Warfarin is an anticoagulant.

It is most likely to be the drug popularly referred to as a "blood thinner," yet this is a misnomer since it does not affect the thickness or viscosity of blood. Instead, it acts on the liver to decrease the quantity of a few key clotting factors in the blood that allow blood to clot.

Warfarin is effective and relatively safe for preventing thrombosis and embolism (abnormal formation and migration of blood clots) in many disorders. It was approved for use as a medication in the early 1950s and has remained popular ever since; warfarin is currently the most widely prescribed oral anticoagulant drug in North America.

Despite its effectiveness, treatment with warfarin can be complicated. Many commonly used medications interact with warfarin, as do some foods (particularly plants containing vitamin K), and its activity has to be monitored by blood testing for the international normalized ratio (INR) to ensure an adequate yet safe dose is taken. A high INR predisposes to a higher risk of bleeding, while an INR below the target range indicates that the dose of warfarin is insufficient to protect against thromboembolic events.

The type of anticoagulation (clot formation inhibition) for which warfarin is best suited is in areas of slowly running blood, such as in veins and the pooled blood behind artificial and natural valves. Thus, common clinical indications for warfarin use are atrial fibrillation (AF), the presence of artificial heart valves, deep venous thrombosis (DVT), and pulmonary embolism (PE).

If you miss your dose of warfarin and realize it before it's time to take your next dose – take it! If it's already time for the next day’s dose, don’t double up. Just continue with your usual regimen.

Tylenol® (acetaminophen/APAP) is OK:
Maximum 2000mg per day while taking warfarin
= 4 extra strength (500mg) tablets
= 6-7 regular strength (325mg) tablets
= 4 Vicodin® (hydrocodone/APAP 5/500) tablets

DON’T use NSAIDs (non-steroidal anti-inflammatory drugs) such as: ibuprofen, naproxen, aspirin (unless prescribed by MD), or aspirin-containing products (like Pepto-Bismol® or Alka Selzer®)

Many medicines can interact with warfarin and change your dose requirements. Some of the most common interactions:

Can Cause an Increase in INR = Lower Warfarin Dose Requirements:

• Sulfamethoxazole/Trimethoprim (Septra/Bactrim)
• Metronidazole (Flagyl)
• Erythromycin
• Fluconazole (Diflucan)
• Amiodarone (Pacerone)

Can Cause a Decrease in INR = Raise Warfarin Dose Requirements:

• Dicloxacillin (Dynapen)
• Rifampin
• Carbamazepine (Tegretol)
• Phenobarbital

Can Increase or Decrease INR:

• Phenytoin (Dilantin)

There are many more potential interactions. Always call to report newly prescribed medications and supplements to your anticoagulation provider.

Many herbal supplements and alternative medicines are not well studied with respect to interactions with prescription medications. Always check with your provider before starting a new non-prescription item.

From the Coumadin package insert:
Caution should be exercised when botanical medicines are taken with warfarin as few studies exist evaluating the potential for interactions.

• Bromelain, danshen, dong quai, garlic, ginkgo and ginseng are often associated with an increase in the effects of warfarin
• CoQ10 and St John’s wort are often associated with a decrease in the effects of warfarin
• Fish oil/omega 3 fatty acids and vitamin E have been associated with increased bleeding when combined with warfarin

Vitamin K is a vitamin (just like vitamin A, B, C, etc) that is found in all foods and your body even makes some vitamin K on its own. (It is not potassium—this is abbreviated K+).

Vitamin K is found in large amounts in green leafy vegetables (such as spinach, broccoli and brussel sprouts) and liver meats, as well as fats and dressings (such as canola oil, soybean oil, margarine and mayonnaise).

You do not need to change what you eat: Just be relatively consistent with foods that contain high amounts of Vitamin K.

Nosebleeds are common for patients on anticoagulation, especially during dry weather.

If you experience a nosebleed, sit down and lean your head slightly forward. Apply pressure or pinch the nostrils for about 15 minutes (breathe through your mouth).

A cold compress applied in the nasal area can also help slow or stop the bleeding.

Avoid carrying heavy items or lowering your head below your heart.

Try using a saline nasal spray to treat dryness in the nostrils and prevent future nosebleeds.

For small cuts and scrapes, apply light pressure or compression with a clean cloth or gauze. If necessary, elevate the affected area above the heart. A cold compress can also help stop the bleeding.