What Is Warfarin?

Date: Jun-01-2013Warfarin is an anticoagulant medication - it is used to slow down the blood-clotting process. Anticoagulants are used to prevent blood clots which may cause vein blockages, heart attack and stroke.

Warfarin is known under the brand names Warfant, Jantoven, Coumadin, Lawarin, Marevan, and Waran.

Doctors prescribe warfarin for people who are at a higher risk of forming blood clots. Examples include patients with..:
..blood clots in the veins of the legs (deep vein thrombosis)
..a blood clot in the lungs (pulmonary embolism)
..an irregular heart beat (atrial fibrillation). A study showed that for older atrial fibrillation patients, warfarin is better than aspirin to reduce stroke risk
..a replacement or artificial heart valve

Warfarin started off as a pest-killer
Warfarin was first used in 1948 as a pesticide to kill mice and rats. In fact, it is still popular for pest control today.

In the 1950s, researchers found that it helped prevent thrombosis and embolism in many illnesses and disorders. In 1954, it was approved in the USA for clinical use in humans.

US President Eisenhower was prescribed warfarin after having a heart attack in 1955. Some historians claim that Joseph Stalin, the Soviet Leader, died after being poisoned with warfarin. In very high doses, warfarin causes multiple hemorrhages.

Warfarin has remained popular for nearly sixty years, and is today the most widely prescribed anticoagulant in the USA, Canada, Western Europe and Australasia.

Warfarin is the most widely-prescribed anticoagulant
The word warfarin comes from the acronym WARF (Wisconsin Alumni Research Foundation), the organization which funded key research into the anticoagulant, and -ARIN, indicating its link with coumarin.

Coumarin is used by pharmaceutical companies as a precursor molecule in the synthesis of many synthetic anticoagulants, including warfarin (brand name Coumadin).
How does warfarin work?
To be able to clot our blood needs vitamin K. Warfarin slows down vitamin K production in the body, thus slowing down the blood clotting process (increases how long it takes for the blood to clot).

Warfarin helps the blood flow more freely around the body and makes it less likely that clots form in the heart or blood vessels.
What are the disadvantages associated with Warfarin?
Warfarin interacts with some foods, drugs and supplements

In spite of being an effective medication, warfarin has several disadvantages. Many prescription drugs and foods interact with warfarin.
Foods with high levels of vitamin K1 interact with warfarin. Examples include liver, broccoli, Brussels sprouts, and green leafy vegetables (coriander, cabbage, collards, spinach, Swiss chard). If you are on warfarin, check with your doctor if you are considering a radical change in your diet.

Researchers from the Intermountain Medical Center Heart Institute found that of the 100 most popular OTC herbal/dietary supplements, over two-thirds interfered with how Warfarin worked. The team interviewed 100 atrial fibrillation patients and found that 35 were taking supplements while on Warfarin. 54% of them were not aware of any interaction risk. The supplements compete with the anticoagulant medication in the liver, altering the way it works, making warfarin either under- or over-active, so that the blood becomes either too thin (raising the risk of bleeding) or too thick (increasing the risk of stroke).

According to Health Canada, the following mineral, herbal and vitamin products can alter levels of warfarin in the bloodstream or might directly affect blood clotting on their own: Vitamin K, Vitamin A, St. John's Wort (hypericum perforatum), Papaya extract (with papain), Methyl salicylate
Lycium barbarum, Horse chestnut (aesculus hippocastanum), Green tea, Ginseng, Ginkgo biloba, Fish oil supplements containing EPA and DHA, Feverfew (tanacetum parthenium), Fenugreek with boldo (peumus boldus), Dong quai (angelica sinensis), Devil's claw (harpagophytum procumbens), Danshen (salvia miltiorrhiza), Coenzyme Q10 (ubiquinone, ubidecarenone) and Chondroitin plus glucosamine.

The following medications are known to interact with warfarin:
Acetaminophen (paracetamol, Tylenol)
Antibiotics (tetracycline azithromycin, erythromycin)
Antidepressants (paroxetine, fluoxetine, sertraline)
Antifungal agents (itraconazole)
Lipid lowering agents (fibrates, statins)
Non-steroidal anti-inflammatory agents (celecoxib, acetylsalicylic acid)
Stomach ulcer / acid reducing agents (cimetidine, ranitidine, omeprazole)
Warfarin's Product Monograph includes warnings regarding interactions with these medications.

Patients on warfarin need to have regular blood tests

Patients on warfarin have to be monitored carefully. Their blood needs to be regularly tested for their INR (international normalized ratio) to make sure the dosage taken is just right. If the INR is high there is a risk of bleeding, while a low INR increases the likelihood of a *thromboembolic event. Initially, the patient's blood will probably be tested daily, and then later about once or twice a week.

*Thromboemolism is the formation of a clot (thrombus) in a blood vessel that breaks loose and travels in the bloodstream to eventually plug another vessel. The thrombus may plug a vessel in the lungs (pulmonary embolism), brain (stroke), leg, kidneys or the gut. Thromboembolic events cause millions of deaths and diseases in the USA, especially in adults. Treatment usually involves drugs to widen and relax the blood vessels (vasodilators), anticoagulants such as warfarin, and aspirin.

An article published in the August 2011 issue of NEJM (New England Journal of Medicine) explained that atrial fibrillation patients may be better off with rivaroxaban than warfarin, because rivaroxaban is easier to administer and requires much less monitoring.

Although effective alternative anticoagulant medications to warfarin which are easier to administer, do not require regular drug testing, have fewer interactions with other drugs exist, experts believe warfarin will continue to be the leading treatment for patients with atrial fibrillation. The main reason is cost - the new antithrombotic drugs are extremely expensive.

Bleeding in the brain

Researchers from the University of Cincinnati reported in the journal Neurology (September 2008 issue) that patients on warfarin may have larger amounts of bleeding in the brain

Bone fracture risk

Very elderly patients who take warfarin have a higher risk for osteoporosis-linked bone fracture, according to a study carried out at Washington University School of Medicine in St. Louis. The investigators say that doctors need to carefully monitor the bone health of their older patients when they are on anticoagulant medication.
Who should avoid or be careful with warfarin?
Avoid warfarin

Patients with severe hypertension (very high blood pressure) should not take warfarin
If you have a peptic ulcer you should avoid warfarin
Pregnant women should avoid warfarin because it passes through the placental barrier and may cause bleeding in the fetus. Warfarin during pregnancy also increases the risk of preterm birth, neonatal death, stillbirth, and spontaneous abortion.
Use warfarin with caution

Patients with the following problems or circumstances should use warfarin with caution, according to the National Health Service, UK:
Hemophilia and other bleeding problems
Liver problems
Kidney problems
Very elderly patients
Patients who recently had surgery
What are the side effects associated with warfarin?
The two most serious side effects of warfarin are gangrene and internal bleeding. Patients on anticoagulant medications need to look out for excessive bleeding (hemorrhages). If you experience any of the following tell your doctor immediately and have an urgent blood test:
Vomiting with blood
Passing blood in urine
Passing blood in stools (feces)
Excessive bruising
Coughing up blood
Bleeding gums
Heavy or excessive bleeding during your menstrual period
Bleeding from the vagina when a menstrual period is not due

The following side effects are also possible (less common):
Diarrhea
Hair loss
Skin rash
Feeling sick (wanting to vomit)
Vomiting

Patients who experience jaundice should tell their doctor immediately.
Higher risk of death after injury for patients taking warfarin
Patients on warfarin may have a higher risk of death after a traumatic injury than other people of the same age, according to an article published in Archives of Surgery (January 2011 issue).

Lesly A. Dossett, M.D., M.P.H., of Vanderbilt University Medical Center, Nashville, Tenn., and team gathered and examined data on over 1.2 million people who had been admitted to trauma centers between 2002 and 2007. They found that 9.3% of warfarin users died from their injuries after a traumatic event, compared to 4.8% of other people of the same age.

The study also found that patients on warfarin were more likely to have blunt mechanism injuries and had a higher risk of sustaining their injuries at home or some residential institution - overall, warfarin users experience more severe injuries.

The researchers added:

"The most profound impact is among younger patients with head injuries," the authors write. "While older patients with severe head injuries have high mortality rates whether or not they are warfarin users, warfarin use increases the mortality from severe head injuries by 50 percent in patients younger than 65 years.

"These data support other reports that suggest that patients who undergo pre-injury anticoagulation with warfarin are at increased risk of death after trauma. Warfarin prescribers should consider these data in the overall risk-benefit analysis when opting to prescribe warfarin, and these data provide further rationale for discontinuing warfarin when the clinical evidence no longer supports its use."

A pharmacist explains how Coumadin (warfarin) works

Written by Christian Nordqvist

View drug information on Cimetidine Hydrochloride Oral Solution; Ranitidine Capsules; Warfarin Sodium tablets.

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