What are they
Anticoagulants are drugs that reduce blood coagulability. Their function is to interfere with hemostasis, that complex of physiological reactions that serve to block bleeding.
Their usefulness concerns the conditions in which these reactions are activated in a pathological way, determining the formation of thrombi (agglomerates of coagulated blood) inside the blood vessels.
Together with antiplatelet agents and fibrinolytics, anticoagulants therefore fall into the category of antithrombotic drugs.
How they work
Hemostasis is a process consisting of two successive steps: the aggregation of platelets and the synthesis of fibrin (which corresponds to the actual coagulation).
Fibrin is a protein formed by filaments intertwined together to form a kind of network – which has the function of trapping blood cells (platelets, red blood cells and white blood cells) – and is the final product of the so-called “coagulation cascade”.
This cascade is a sequence of linked biochemical reactions in which specific compounds (coagulation factors) normally present in the blood in inert form are activated, one after the other.
The different anticoagulant drugs intervene in different stages of the coagulation cascade preventing its completion.
What are they?
Anticoagulants are distinguished depending on their mechanism of action into two classes: direct anticoagulants and indirect anticoagulants.
| Active ingredients | Mechanism of action | |
|---|---|---|
| Direct anticoagulants | Heparin, synthetic analogues of hirudin, argatroban | Inhibit the action of some of the coagulation factors present in the circulation |
| Indirect anticoagulants | Warfarin, acenocoumarol | Counteract the activation of vitamin K |
Let’s see them in detail.
Direct anticoagulants inhibit the action of some of the coagulation factors present in the circulation. The prototype of this category is heparin, a molecule that in mammals is normally produced by various tissues of which, today, some fractions synthesized in the laboratory, known as “low molecular weight heparins”, are used more often.
The other active substances belonging to this category – synthetic analogues of hirudin (a molecule present in the saliva of leeches) and argatroban – are used only in case of contraindications to heparins.
The direct anticoagulants mentioned are intended exclusively for parenteral, intravenous or subcutaneous administration, and given their intervention on coagulation factors already present in the blood, they have immediate effect.
Recently introduced, and currently approved only for the prevention of deep vein thrombosis in patients undergoing orthopedic surgery, is dabigatran, a direct anticoagulant suitable for oral administration.
Indirect anticoagulants act upstream: they counteract the activation of vitamin K, which is involved in the synthesis of some of the coagulation factors by inhibiting their production. The main ones belong to the category of dicumarolics, within which the two most used active ingredients are warfarin and acenocoumarol.
As an alternative for selected cases there are indandionici (phenindione).
Indirect anticoagulants are intended for oral administration, and given their mechanism of action they take effect only after an interval of a few days (equal to the time necessary for the degradation of the factors already in circulation at the time of the first administration).
When using
Anticoagulants are used to reduce the risk of thrombosis in: – patients with venous diseases – patients subject to prolonged immobilization – patients undergoing surgery – patients with atrial fibrillation – patients with heart valve prostheses – patients with unstable coronary artery disease.
In general, parenteral therapy with direct anticoagulants is used when the risk of thrombo-embolism is acute (or during pregnancy) and oral therapy with indirect anticoagulants when the risk is chronic.
How to use them
The fundamental goal of oral anticoagulant therapy is to inhibit blood coagulability in the long term to achieve the highest possible protection from thromboembolic accidents without increasing the risk of bleeding too much.
The degree of optimal coagulation inhibition, called “therapeutic range”, varies according to the pathological conditions. To assess the achievement of the therapeutic range – and therefore determine the effectiveness of the therapy and possibly correct the dosage – a blood coagulability index, the INR (International Normalized Ratio), is used, which must be measured regularly during treatment.
Precautions
In addition to careful monitoring of INR, anticoagulant therapy requires certain precautions, especially with respect to a number of conditions that can interfere with their effects.
Among these, the intake of other medicines (there are many drugs, even in common use, and herbal preparations that interact with anticoagulants), the intake of high amounts of vitamin K with the diet, the consumption of alcohol, the onset of other diseases (diarrhea, fever, liver disease, thyroid dysfunction).
The increased bleeding risk during anticoagulant therapy should be considered in anticipation of surgery, tooth extractions and endoscopic investigations.
Oral anticoagulants are absolutely contraindicated during pregnancy, as they can cause fetal malformations.
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
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