Warfarin vs Heparin: Similarities and Differences

Often, the term blood clots may have a negative connotation as they are associated with health complications like PE (pulmonary embolism) and heart attack. However, that’s not entirely true. In fact, blood clotting is an essential process in the body. Blood clotting is necessary to stop bleeding and seal wounds at the site of injury; this is how blood clots are supposed to function. However, it becomes very dangerous and even life-threatening when these blood clots are formed within blood vessels or when they break free and travel to another part of the body. When this happens, these blood clots can cause blockage in your circulatory system, causing stroke and heart attack.

Warfarin and heparin are some of the most commonly prescribed anticoagulants or “blood thinners'' that interrupt the blood clotting process. Keep in mind heparin is short for unfractionated heparin (UFH). They are used to treat conditions such as venous thromboembolism (VTE) and pulmonary embolism (PE), which are blood clots in the blood vessels and lungs, respectively. Please continue reading to learn more about these anticoagulant medications, such as the similarities and differences between heparin versus warfarin. In this article, when the term heparin is mentioned, it is indeed unfractionated heparin (UHF) that is referred to.

How does warfarin work?

Warfarin (brand names Coumadin, Jantoven) is a vitamin K antagonist. Warfarin works by blocking the function of vitamin K epoxide reductase (VKOR) in the liver. When vitamin K is consumed through oral intake, such as green leafy vegetables, VKOR converts vitamin K into a different form of vitamin K that helps to activate the clotting factors. In other words, by interfering with VKOR’s function, warfarin reduces the production of Vitamin K-dependent clotting factors, preventing the formation of blood clots.

What is heparin and low-molecular-weight heparin?

Both heparin and low-molecular-weight heparin (LMWH) are anticoagulants or blood thinners that work to make it harder for blood to clot. Though heparin and LMWH share many similarities, including what they’re used for, there are differences in how they work, specifically, which clotting factors they target.

Heparin is an anticoagulant that causes the inactivation of thrombin and prevents the conversion of fibrinogen to fibrin. This medication prevents blood clots from forming and stops blood clots that have already formed from becoming larger. Heparin can be administered through a subcutaneous (under the skin) injection or intravenous (into the vein) infusion.

Low molecular weight heparin (LMWH) are anticoagulants that have anti-factor Xa (10a) and anti-thrombin (anti-factor IIa) activities. Factor Xa and factor IIa are two of the natural enzymes in the body that form blood clots. By acting on the clotting factors, LMWHs reduce thrombin production, preventing blood clot formation. Enoxaparin (Lovenox) is a commonly-prescribed LMWH. Other agents in this drug class include Fragmin (dalteparin) and Innohep (tinzaparin).

What conditions are anticoagulants used to treat?

Anticoagulants are used to treat and prevent the following conditions that are caused by a blockade in the circulatory system.

Deep vein thrombosis (DVT) and pulmonary embolism (PE)

Anticoagulants are used to treat or prevent a blood clot in the blood vessels (deep venous thrombosis) or lungs (pulmonary embolism). When a blood clot is formed in one or more of the deep veins in the body, DVT happens as a result. DVT usually takes place in the legs. On the other hand, a PE happens when a blood clot causes a blockage in an artery in your lungs. If a severe PE is left untreated, it can be fatal.

Stroke

A stroke happens when a blood clot migrates to your brain and causes blockade in the smaller blood vessels.

Heart attack

Myocardial infarction (MI) is the medical term for heart attack. Myocardial infarction can happen when a blood clot blocks the blood supply to the heart. Same as stroke and PE, a heart attack (myocardial infarction) can be fatal.

If you have one of the following health conditions, your risk of developing a blood clot is higher. As a result, these health problems can put you at higher risk for stroke, heart attack, or MI. Therefore, taking an anticoagulant will help lower this risk.

Atrial fibrillation (AFib)

Atrial fibrillation, or AFib, is a heart rhythm disorder. This heart condition begins in the atria, the upper chambers of your heart. If you have AFib, the heart’s electrical impulses are interrupted, causing a fast, irregular heart rhythm. When the atrium is beating too fast, they lose effectiveness, causing blood to pool. This can lead to a blood clot as the pooling blood stays stagnant. A blood clot from your heart can dislodge and migrate to your brain and cause a stroke.

Surgery for hip or knee replacement

Hip or knee replacement surgery can put you at an increased risk of developing a deep vein thrombosis (DVT). The surgery team will decide which anticoagulant is appropriate for you.

Certain types of heart surgery

When you have surgery to replace your heart valve, you are at higher risk of forming a blood clot at the new valve. Your cardiologist will determine the type of anticoagulant that is the best option for you.

Genetic blood clotting disorders

Examples of some inherited blood clotting disorders are Factor V (factor 5) Leiden, Prothrombin 202010 Mutation, Protein S Deficiency, and Protein C Deficiency. People with inherited blood clotting disorders tend to develop blood clots before 45 years of age.

What are the similarities between heparin and warfarin?

Both heparin and warfarin are prescription anticoagulant medications. They are used to prevent and treat blood clots in conditions such as deep vein thrombosis, pulmonary embolism, and atrial fibrillation and in people with mechanical heart valves. Both warfarin/heparin share some similar drug interactions. Also, both carry a high risk of adverse events such as bleeding complications.

What is the difference between heparin and Coumadin?

The key differences between heparin and Coumadin (warfarin) are as follows:

Warfarin and heparin work differently. Warfarin works by depleting the functional vitamin K reserves, in turn, interfering with the production of vitamin K-dependent clotting factors which are factors II, VII, IX, and X, along with protein C and protein S. Heparin not only works by blocking the conversion of fibrinogen to fibrin, a substance needed for clot formation but also inhibits the activation of platelets and of Factors V and VIII.
After a myocardial infarction or heart attack, heparin is given by subcutaneous (under the skin) injection or intravenous (IV or into a vein) infusion in the hospital. Warfarin is an anticoagulant option to be taken by mouth once the patient is discharged home.
Heparin’s onset of action is faster (it starts working more quickly than warfarin), but this immediate effect wears off when you stop receiving the medicine.
Warfarin is available as an oral tablet. Heparin and low-molecular-weight heparin (LMWH), such as Lovenox, are given as a subcutaneous (under the skin) injection. Heparin can also be administered via an intravenous (into the vein) infusion.
Warfarin levels are adjusted to achieve a target international normalized ratio (INR) in the therapeutic range (this is a blood test that measures how long it takes for a blood clot to form). The INR goal differs based on the condition being treated. For example, an INR range between 2 and 3 is desirable for someone with Afib, while someone with a mechanical mitral valve replacement would aim for an IRN range between 2.5 and 3.5. The dose of heparin is based on the patient’s body weight and the condition being treated.
Warfarin is used for long-term treatment, ranging from several months to indefinitely. Heparin is typically used for a few days, up to a week.
Taking warfarin is not recommended for pregnant women as it can result in birth defects and bleeding problems in the baby. Low-molecular-weight heparin (LMWH) and unfractionated heparin are the anticoagulants of choice in pregnant women and women who have given birth.
Some of the adverse effects of the two medications are different. For example, warfarin can cause hair loss. Heparin is associated with a life-threatening condition called heparin-induced thrombocytopenia.

Are there antidotes for heparin and warfarin?

The antidote for unfractionated heparin is protamine sulfate. This drug is also partially effective against low molecular weight heparin. The antidote for warfarin is vitamin K.

What is the difference between warfarin and enoxaparin?

One of the key differences between warfarin and enoxaparin is that during long-term therapy with warfarin, you need to get regular blood tests. This is to check lab values of the international normalized ratio (INR) and ensure it is at a therapeutic level. Treatment with low-molecular-weight heparin (LMWH), such as enoxaparin (Lovenox), does not require regular blood tests because these drugs have more predictable anticoagulant effects.

Which is right for me - heparin or warfarin?

Your healthcare provider will determine which anticoagulant medication is right for you - heparin vs warfarin. The choice depends on several factors, such as your medical history, including kidney function and complications like heparin-induced thrombocytopenia (HIT), prior clotting events, and previous treatments.

Generally speaking, a blood clot (venous thromboembolism or pulmonary embolism) is managed with both heparin and warfarin. The initial anticoagulant used is heparin because it has a quick onset of action. In some cases, patients are given a loading dose of heparin, followed by a maintenance dose of heparin in the inpatient setting. In the meantime, warfarin therapy is started, and blood tests such as prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR) are done to check if they are at therapeutic levels. Patients can typically go home once they have been transitioned from heparin to warfarin. The transitioning process from heparin to warfarin is called “bridging” when heparin is overlapped with warfarin until the effect of warfarin is demonstrated. Bridging usually takes 5 to 6 days, with at least 48 hours of the INR in the therapeutic range. As mentioned, the INR ranges may differ between people depending on the condition being treated. Also, there is no guideline for the bridging regimen; the criteria for bridging is usually determined through hospital policy.

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