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Heparin: Pharmacology & Pharmacokinetics

Instructor: Charity Hacker

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

Heparin can be a life-saving medicine, but it can also be a very dangerous medicine if used incorrectly. Before anyone in the health care field administers heparin, they should know all about it. In this lesson, you will learn all about the pharmacology and pharmacokinetics of heparin.

All About Heparin

Imagine you are a nursing student and your assigned patient for the next day is on a heparin drip. You need to know all about this drug before you show up for clinicals the next day. You need to know the pharmacology: origin, drug class, mechanism of action, and its pharmacokinetics. Pharmacokinetics is how a drug moves through your body: how does your body absorb, distribute, metabolize, and eliminate the drug?

Pharmacology

You decide to start your inquiry at the beginning. Where did heparin come from? You find that the discovery and development of Heparin began over 100 hundred years ago at John Hopkins University in the year 1916. Although it was discovered at that time, it was continuously researched and refined until it reached a point of consistent mass production in the 1949.

You discover that heparin is an anticoagulant. An anticoagulant is something that interrupts the clotting process. It is often used prophylactically to prevent venous thrombosis or pulmonary emboli, or atrial-fibrillation related emboli, in other words, blood clots. It can also be used during medical procedures, such as dialysis or surgery.

Heparin does not dissolve blood clots. It disrupts the anticoagulation process, known as the coagulation cascade at multiple sites. Specifically, it inhibits coagulation factor Xa. The little a means activated. Coagulation factor X, when activated, is the key stimulus for Prothrombin in both the intrinsic and extrinsic pathways. Heparin does this by enhancing the action of ATIII, an antithrombin. Antithrombins inhibit the action of thrombins, in this case factor Xa.

Pharmacokinetics

Okay, so you understand heparin's history, what it does, and how it does it, but what do you need to know about in relation to your patient? Let's look at the pharmacokinetics to get a better picture.

Absorption

First and foremost, it absorbed best parenterally. Parenterally means by injection. Heparin is best absorbed by intravenous administration. However, although its absorption is not consistent with subcutaneous administration, it is used that way as a prophylaxis. When heparin is administered via IV, it begins working immediately and is at peak concentration immediately. Subcuteaneous action is delayed 20-60 minutes. What does this mean to you and your patient? Although, heparin does have an antidote, you need to check and double check your dose before administering heparin.

Distribution

Heparin is transported through the body by many major blood components. It binds to clotting factors such as antithrombin and fibrinogens. Components such as lipoproteins (fat transporters), proteases (enzymes that break down proteins), and globulins are also sites of heparin binding and help it get where it needs to go. The volume of distribution, a key pharmacokinetic number used by pharmacists, is 0.07 Liters per Kilogram.

Metabolization

In general, the metabolization of heparin is not well-known. Most literature agrees that it is partially metabolized in the liver and the reticuloendothelial system. What is the reticuloendothelial system? It is part of the immune system, consisting partially of macrophages. Macrophages are white blood cells that wrap around and then destroy foreign bodies.

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