Anticoagulant Medications
Preventing Clots With Blood Thinners

Heart Health Medications


Anticoagulant Medications


What Are Anticoagulants?
How Do They Work?
When Are They Used?
What Are The Side Effects?
Advice For Patients Taking Anticoagulants

Main Guide:
Heart Disease in Women

Other Heart Meds:

ACE Inhibitor Drugs
Aspirin Therapy
Beta Blockers
Calcium Channel Blockers
Thrombolytic Therapy

Potential Complication:
Woman with severe warfarin necrosis of the breast

Related Articles:

What is blood?
How does blood clot?

What Are Anticoagulants?

Also called blood thinners, anticoagulants are a group of drugs which make it more difficult for blood to clot. They are used to treat thrombosis and occasionally to treat or prevent stroke. They are also prescribed to long-term to patients who have undergone major surgery (especially heart bypass surgery) or during hemodialysis (kidney dialysis). Although there are a number of different anticoagulants, the most common are heparin and newer heparin derived medications such as tinzaparin - all of which have to be given by injection; and warfarin which is taken orally as a pill. Initially most patients may be given heparin but it is withdrawn when warfarin kicks in and becomes effective. Warfarin is the preferred medication because it is a pill, it is less expensive and doctors are more familiar with it.

Common Brand Names

Generic Drug Name Brand Name
Warfarin Coumadin; Jantoven; Marevan; Lawarin; Waran; Warfant
Heparin Hep-Pak; Heparin Lock Flush; Hep-Pak CVC; Hep-Lock; Heparin Sodium ADD-Vantage
Low Molecular Weight Heparin (LMWH) Fragmin; Lovenox; Innohep (tinzaparin)
Direct Thrombin Inhibitors


Argatroban (same as generic name);
Angiomax; Angiox
Factor Xa Inhibitors



How Do They Work?

Anticoagulants work by reducing the activity of certain enzymes (proteins) known as blood clotting factors. These factors are necessary for the blood to clot. The drugs do not dissolve existing clots which have already formed - these can be treated with thrombolytics. However they can stabilize an existing clot so that it does break away and cause an embolism (an artery blockage caused by a blood clot). Although anticoagulants are commonly called blood thinners, they do not in fact thin the blood but rather reduce the blood's ability to clot. While antiplatelets (such as aspirin) also prevent blood clots from forming - they work in a different way. Antiplatelet drugs block platelets while anticoagulants interfere with the enzymes in the blood necessary for clotting. Anticoagulants such as warfarin are much stronger than antiplatelets so a patient taking them will need to be frequently monitored by their doctor. The doctor will perform a regular blood test to check for clotting factor, this is critically important for preventing bleeding complications and ensuring that enough clotting ability still remains. Some clotting ability is important because if the patient cuts their hand, the blood needs to be able to clot at the point of the wound, otherwise they will continue to bleed.

How Different Types Of Anticoagulants Work

How Warfarin Works
Warfarin works by blocking the effect of vitamin K. The liver uses vitamin K to produce the protein enzymes which are needed for blood clotting. By blocking the effect of vitamin K, warfarin makes it more difficult for these enzymes to be produced so that it becomes more difficult for the blood to clot.

How Heparin Works
Heparin is a substance which is derived from the intestines of pigs. Low Molecular Weight Heparin (LMWH) are newer medications such as tinzaparin (brand name Innohep) which are derived from heparin. Heparin needs to be injected with an IV in hospital whereas LMWH can be injected directly under the skin, much like a diabetic insulin shot. Both heparin and LMWH work by activating a protein enzyme called antithrombin 3. This enzyme is part of the body's natural anti-clotting system which stops the blood clotting when it should not. Antithrombin 3 is a key component in this system as it blocks one of the vital steps in the clotting process.

Direct Thrombin Inhibitors
Drugs such as argatroban and bivalirudin are known as Direct Thrombin Inhibitors. They work by blocking the action of thrombin, a protein enzyme which is necessary for one of the steps in the blood clotting system. Bivalirudin is often used to treat heart attack patients and argatroban is used to treat people with blood clots in the lung or legs (thrombosis) and who also have an allergy to heparin.

Factor Xa Inhibitors
These anticoagulants (most common drug is fondaparinux) are used to block the action of Factor Xa, like thrombin, an essential protein in the process of blood clotting. It is mostly prescribed to patients to prevent lung or leg blood clots after major surgery (for example those with hip arthritis who undergo hip replacement surgery) but it may also be given to people having a heart attack.

When Are They Used?

The main reason for the use of anticoagulants (in particular warfarin) is to treat:

Atrial Fibrillation (AF)
A type of heart arrhythmia, atrial fibrillation (AF) causes irregular and fast heartbeats and is usually found in patients with coronary heart disease (CHD). If a blood clot forms as a result of AF it can lead to stroke in women.
Many patients with AF take both antiarrhythmics and an anticoagulant.

Deep Vein Thrombosis

Blood clots which form in the legs or lungs. This can be caused by major surgery, prolonged sitting or bed rest, pregnancy and obesity. If a blood clot forms in the legs it can travel to the lungs and cause pulmonary embolism (PE). Severe cases of PE can lead to sudden death.

Artificial Valves
Patients with artificial mechanical heart valves are at risk of embolism and the risk is even greater if they suffer atrial fibrillation. They may be prescribed anticoagulants long-term.

Heart Attack Patients
Those who have suffered a heart attack are at greater risk of developing a clot at the site where the original clot was dissolved by thrombolytic therapy. If the left ventricle was damaged by the heart attack, a clot may also develop there and cause another heart attack. Doctors sometimes prescribe warfarin to prevent these complications. If the patient is in bed for a long time after a heart attack, the drug will also help prevent blood clots in the legs. If the patient is having a heart attack then they may be treated with heparin/LMWH, Factor Xa Inhibitor or a thrombin inhibitor (never warfarin). Heparin, which is administered by IV in hospital, is a powerful anticoagulant. It is also sometimes given to patients after heart angioplasty. The dosage must be carefully monitored. The new types of heparin (LMWH) require less monitoring. If you have had a heart attack, check out our section on heart attacks books. There are many things you can do to reduce your risk of a second episode.

What Are The Side Effects?

Hemorrhagic Bleeding
Bleeding, particularly in the brain, is the side effect which causes most concerns for doctors. One study showed that between 2 and 22 percent of patients treated with oral anticoagulants because of ischemic cerebrovascular disease (blockages in the arteries due to fatty deposits called atherosclerosis) developed major bleeding complications. The bleedings were fatal in up to 9 percent of those cases. Bleeding is a risk because anticoagulants interfere with the way in which the blood clots. Those taking warfarin need regular blood tests and monitoring to check for signs of problems. Mixing warfarin with aspirin or alcohol can increase the risk of bleeding.

Skin Necrosis
A small number of patients (1 in 10,000) taking warfarin develop a severe skin rash called warfarin necrosis. If it occurs, it usually does so within 2 to 5 days of starting therapy. It tends to affect areas of the skin which have a higher fat content such as the thighs, breasts, hips, buttocks and abdomen. The first sign is a painful purple rash which over a few days becomes bluish black like a bruise. It may also have a red rim. It then develops into blood blisters and the area of skin dies (necrosis). The main treatment is stop the use of warfarin. If anticoagulants are still needed, heparin might be prescribed. Sometimes vitamin K is used to reverse the effects. Once warfarin is stopped, small areas can heal naturally. However if it caused large areas of necrosis, then skin grafting surgery may be necessary.

Taking warfarin increases a person’s osteoporosis risk factors. This is because the drug interferes with vitamin K which is involved with the protein osteocalcin and osteocalcin is needed for bone formation. One extensive study of 15,000 patients found that long-term use of warfarin (longer than one year) led to a 25 percent increase in the amount of bone fractures. Those who took the drug for less than a year showed no increase in risk. Patients taking warfarin should exercise regularly and ask their doctor about taking a vitamin D and calcium supplement to maintain bone strength (see also osteoporosis prevention tips).

Advice For Patients Taking Anticoagulants

• Talk to your doctor about ensuring treatment only lasts as long as is necessary.
• Have regular blood tests to check that the drugs are working.
• Never take aspirin with anticoagulants unless told to do so by your doctor.
• Always check with your doctor before taking any other drugs or food supplements. This includes vitamins, flu medicines, pain killers, sleeping pills and antibiotics. These can alter the strength of anticoagulants, making them stronger or weaker.
• Talk to your doctor about a specific eating plan. For example, green tea and parsley should be avoided.
• Always carry an emergency medical ID card on you stating that you are taking anticoagulants. Tell your family how you take your medication and in what dosage.

• Useful article: Living with Heart Disease.

When To Contact The Doctor

The following are signs which require immediate medical attention:

• Urine turns red or pink.
• Stool becomes dark brown, black or red.
Heavy periods - bleeds that are heavier than normal.
• Increased bleeding from the gums when brushing your teeth.
• Severe headaches, difficulties breathing or stomach pain that do not go away.
• Feeling sick, weak or faint.
• Blood seen with vomiting or coughing.
• You develop bruises or blood blisters.
• Bleeding from a cut or the nose that does not stop within 5 to 10 minutes.
• You have an accident of any kind.
• You find out that you are pregnant. (Heart disease in pregnancy)

  Related Articles on HEART DISEASE in Women

For more heart related information, see the following:

Risk Factors for Heart Disease
Heart Disease Testing

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