Introduction

Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where they help keep the bite area unclotted long enough for the animal to obtain some blood. As a class of medications, anticoagulants are used in therapy for thrombotic disorders.

Oral anticoagulants (OACs) are taken by many people in pill or tablet form, and various intravenous anticoagulant dosage forms are used in hospitals. Some anticoagulants are used in medical equipment, such as sample tubes, blood transfusion bags, heart-lung machines, and dialysis equipment. One of the first anticoagulants, warfarin, was initially approved as a rodenticide.

Blood clot

Within seconds of cutting a blood vessel, the damaged tissue causes tiny cells in the blood (platelets) to become sticky and clump together around the cut. These activated platelets and the damaged tissue release chemicals which react with other chemicals and proteins in the blood, called clotting factors. There are 13 known clotting factors which are called by their Roman numbers - factor I to factor XIII.

A complex cascade of chemical reactions involving these clotting factors quickly occurs next to a cut. The final step of this cascade of chemical reactions is to convert factor I (also called fibrinogen - a soluble protein) into thin strands of a solid protein called fibrin. The strands of fibrin form a meshwork and trap blood cells and platelets, which form into a solid clot.

Uses of anticoagulants

Anticoagulants are prescribed if you already have a blood clot, the most common cause being a deep vein thrombosis (DVT) and/or a clot on the lung, called a Pulmonary Embolus (PE). in these cases, they prevent the clot from becoming bigger. The other reason they are used is if you are at risk of having a blood clot (prevention).

Anticoagulants may be used to treat blood clots, or in conditions where the risk of blood clots is increased to reduce the risk. Examples of conditions where anticoagulants may be used include: Atrial fibrillation, Deep vein thrombosis (DVT), Hip or knee replacement surgery, Ischemic stroke, Myocardial infarction (heart attack), pulmonary embolism and unstable angina.

Side effects

There are a number of possible side-effects with anticoagulants and it is not possible to list all of these here. However, the major side-effect of all anticoagulant medicines is bleeding. People who take warfarin, acenocoumarol and phenindione need to have regular blood tests to measure how quickly the blood clots.

See the leaflet that comes with your particular brand for a full list of possible side-effects and cautions. These medicines sometimes react with other medicines that you may take. So, make sure your doctor knows of any other medicines that you are taking, including ones that you have bought rather than been prescribed.

Drug interactions

Treatment with more than one blood thinner or using medicine that can cause bleeding will increase the risk of bleeding from any anticoagulant. Antiplatelet medicine such as aspirin and other nonsteroidal anti-inflammatory medications (for example, ibuprofen [Motrin], naproxen [Aleve]), clopidogrel (Plavix), and prasugrel (Effient) can cause bleeding.

Serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac) and paroxetine (Paxil), Garlic and ginkgo also increase the risk of bleeding when combined with another medicine that thins the blood because these herbs can cause bleeding when taken alone. Drug and herbal supplement interactions with warfarin.

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Regards

Mary Wilson

Editorial office

Clinical Pharmacology and Toxicology Research

E-mail: pharmatoxicol@eclinicalsci.com