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Apixaban: Mechanism of Action & Pharmacokinetics

Instructor: Charity Hacker

I am a nursing instructor with over 20 years of nursing experience and a Masters Degree in Nursing Education.

If you want to know all there is to know about a drug, you need to know how it works. It is also important to understand how a drug moves through the human body. In this lesson, we will explore the mechanism of action and pharmacokinetics of apixaban.

Clotting and the Coagulation Cascade

Apixaban is an anticoagulant. Antocagulation inhibits clotting. To understand how any medication that is classified as an anticoagulant works, you must understand the clotting process. Specifically, it is helpful to understand the coagulation cascade. The clotting process can be summarized in just a few steps:

  • Contraction of a vessel
  • Formation of platelet plug
  • Activation of the coagulation cascade
  • Formation of a fibrin clot

Understanding the coagulation cascade will help you understand how apixaban works. The coagulation cascade consists of two pathways, the extrinsic and intrinsic, which consist of all the clotting factors. It is called a cascade because you need one factor to activate the next factor. Imagine the coagulation cascade as a rumor in a big high school. First one or two people hear or see something, then they tell their friends and they tell their friends, and so on. In the cascade, only a few factors are initially stimulated. But, in the end, thousands of factors, are busy at work... clotting blood, not spreading rumors.

Factor Ten, or FX (The X is roman numeral for the number 10), is absolutely essential in the clotting process. It works with Factor Five to stimulate Factor Two. FII, also known as prothrombin, is changed to thrombin when it is activated by FX. Thrombin stimulates Factor One, or fibrinogen, making it fibrin. And what do we know from our review above? Fibrin, or the fibrin clot, is what stops the bleeding in coagulation. Read on to see why this information is important in learning about Apixaban.

Apixaban's Mechanism of Action

Apixaban stops the coagulation process by interrupting the coagulation cascade at FX, actually FXa. What is FXa? When a clotting factor becomes activated by the previous factor in the cascade it is then notated with an a, for activation. Both the intrinsic and extrinsic pathways must pass through the FX and FV junction to stimulate thrombin and then fibrin production. So, to stop this factor, you prevent either pathway from completing the coagulation process.

Pharmacokinetics of Apixaban

Pharmacokinetics is how a drug moves through a body or rather what your body does with a drug once it is inside. This usually encompasses, at a minimum:

  • Absorption
  • Distribution
  • Metabolism
  • Elimination

How Is Apixaban Absorbed?

Apixaban is taken orally, or by mouth. It is absorbed throughout the gastrointestinal track, with over half of the absorption taking place near the end of the small intestine and the beginning of the large intestine. The absorption is not affected by the presence of food. The highest amount of the drug absorbed can be noted three to four hours after administration.

Distribution of Apixaban

The volume of distribution helps you figure out how much of the drug is present in the blood one hour after administration, compared to how much was put in originally. This magic number, volume of distribution, for apixaban is 21 liters. Apixaban comes in 2.5 or 5 mg doses. So, if you draw your patient's blood to determine the amount of apixaban present in his or her blood, you would multiply the result by 21 to see how much of the drug has made it to the blood system. About 50% of the drug administered reaches its ultimate destination of the blood, this is called bioavailability.

Approximately 87% of the administered drug binds to protein. What does that mean and why does it matter? Protein binding can be good and it can be bad. Drugs that are bound to a protein cannot be used, those that are not are called free drugs. Sometimes protein binding is good, because it holds the drug to be used later...like the refrigerator holds food. It takes about three days for apixaban to get to a therapeutic level in the blood.

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