Anticoagulant

An anticoagulant is a medication that helps prevent blood from clotting, or coagulating. Coagulation is when blood cells clump together to form a blood clot, which seals a break or cut in a blood vessel or in the skin. While this is usually a good thing, sometimes these clots can break loose inside a blood vessel and block the flow of blood. This can lead to problems such as stroke. Anticoagulants help prevent these types of clots from forming, and they are often taken by people who are at high risk of forming dangerous blood clots. However, these drugs also increase the risk of bleeding, creating new potential problems. Therefore, physicians must monitor people on anticoagulants closely.

Background

The body is equipped with a number of mechanisms to help protect it. For instance, the immune system protects against harmful viruses and bacteria, and nerves transmit pain signals to warn a person that an object is hot. Another such mechanism is coagulation, a multistep process in which the body attempts to prevent blood loss and infection in the event of an injury or any other break in the body's soft tissues.

When a person sustains a cut, blood leaves through the opening. This immediately starts the process called hemostasis, by which the body works to minimize the amount of blood lost. The process also protects against infection by creating a seal across the broken area. This seal, comprised of blood platelets and a type of protein known as a coagulation factor, forms a clot at the site of the injury.

This is the case even when the injury is internal; for instance, a person who bangs a knee will likely see a bruise develop. This indicates an area where blood leaked from a blood vessel but remained under the skin. Clotting is involved in stopping the bleeding and limiting the size of the bruise.

When these clots are on the skin, they do not usually present any sort of problem. However, sometimes clots form inside the body, either because of an injury, such as a bad bruise or a broken bone, or due to a health condition, such as cancer, pregnancy, or obesity. When one of these clots, called a thrombus, obstructs a blood vessel, it can result in life-threatening consequences.

If blood flow is blocked to a limb, the person is in danger of losing the limb. If the clot travels to the lungs, it is called a pulmonary embolism, and it can block the flow of blood between the heart and the lungs, depriving the patient of oxygen. A blood clot in the brain can cause a stroke, which can kill the person or cause permanent brain damage.

In 1916, a second-year medical student at Johns Hopkins University named Jay McLean was working with William Henry Howell, a Baltimore-born physiologist who was investigating coagulation factors. McLean was working with the livers of dogs when he identified a fat-soluble substance that seemed to cause coagulation. Two years later, Howell named the substance heparin after hepar, the Greek word for "liver." The discovery of this drug predated the establishment of the US Food and Drug Administration, so human trials were not conducted on the medication until 1935. Nevertheless, heparin was found to be safe and effective. It is still in use in the twenty-first century.

Overview

Heparin and other anticoagulants are one of two kinds of medications, sometimes referred to as "blood thinners," that are used to control undesirable blood clotting. The other type of drug is called an antiplatelet medication. Platelets are the component of blood that forms part of a blood clot by releasing a substance called thromboxane, which signals other platelets to come together to form the clot. Antiplatelet medications interfere with this process. While there are several prescription medications in this class, aspirin is one very common antiplatelet medication. This is why people who have had a heart attack or stroke or who are at risk for one are sometimes instructed to take aspirin daily.

Anticoagulants are a stronger medication for preventing clots. Instead of preventing platelets from clumping, anticoagulants prevent the release of substances called clotting factors. These factors are proteins manufactured in the liver. Their production requires vitamin K. Anticoagulants interfere with availability of vitamin K and slow the production of these clotting factors; without them, blood does not clot properly.

Heparin, the first known anticoagulant, is a natural substance. In the decades since it was discovered, other anticoagulants have been developed. These medications include warfarin (Coumadin), rivaroxaban (Xarelto), dabigatran (Pradaxa), apixaban (Eliquis), and edoxaban (Lixiana). Heparin is given by injection, while the newer agents come in oral forms. These medications are available by prescription and require some monitoring by a physician.

Anticoagulants are generally prescribed for people who are at risk of life-threatening blood clots. They are often prescribed for people who are at risk of having a stroke, heart attack, or pulmonary embolism and for people who are at risk of having dangerous blood clots from in the deep veins of the legs, a condition known as deep vein thrombosis (DVT). These clots are dangerous not only because they can impair blood flow and cause damage to the leg, but also because they can break free and cause a pulmonary embolism, which often results in death.

While anticoagulants can be lifesavers, they also have some side effects. Anticoagulants can cause excessive bleeding during any medical procedure, so patients taking these medications should ensure that every physician or dentist they see is aware of their use. They can also lead to severe bruising, blood in the urine or feces, and bleeding gums. In addition, women may have heavy menstrual cycles while taking anticoagulants.

Treatment with these medications can sometimes be short term, but many people need anticoagulants for the rest of their lives. It is important that patients who take them follow instructions and avoid changes to diet and exercise that may require a change in dosage. Changing or adding other medications should be done under the advice of a physician, as some medications can affect how anticoagulants work. Women undergoing anticoagulant therapy who become pregnant or who are considering pregnancy should consult a physician.

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