How anticoagulants prevent clotting of blood

Introduction

     Anticoagulants are agents, which may be natural or synthetic, their function is to inhibit clotting or coagulation. Normally, the body releases certain factors that inhibit those factors which are responsible for clotting. If an injury occurs, then those factors will be activated.

How Anticoagulants Work

     Different anticoagulants may be secreted by the body (natural) or synthetic work in different ways, these ways are given below:

• Anticoagulants work by inhibiting the aggregation of Platelets.
• Anticoagulants prevent blood clotting by inactivating the different clotting factors.
• Anticoagulants work by inhibiting the Glycoprotein IIb/IIIa receptor.
• Anticoagulants prevent coagulation by inhibiting the P2Y12 receptor.
• Anticoagulants prevent clotting by destroying the clot
• Anticoagulants prevent clotting by inhibiting phosphodiesterase

Anticoagulants that are secreted by the body

     The endothelial wall of vessels secretes a compound called Nitric Oxide that prevents the aggregation of platelets, leads to the prevention of clot. The endothelial wall also secrete a compound called Heparin sulfate that binds Antithrombin-III that inactivates Thrombin, Factor-IX, and X. Thrombomodulin is also an anticoagulant that activates protein-C whose function is to inactivates Factor-V and VIII. 

    They function normally to prevent the blood clotting if the vessels are not damaged, and ultimately the damage to the endothelial wall leads to the activation of all these factors bcoz the damaged endothelial wall will be unable to secrete these anticoagulants.

Anticoagulants drugs that prevent blood clotting

     Synthetic anticoagulants are of different types on the basis of their mechanism of action to prevent blood clotting. Following are the different classes of anticoagulants:

1) Indirect Thrombin Inhibitors: This includes all the drugs that indirectly inhibit the thrombin, drugs are Unfractionated Heparin, Low molecular weight heparin (Enoxaparin, Deltaparin), Fondaparinux. These all drugs bind with Antithrombin-III and inhibit the thrombin and factor-Xa.

      If Unfractionated heparin is given, then the patient should be monitored properly through aPTT and PT, as it may lead to the disorders like major is bleeding, also osteoporosis. Protamine sulfate is used to reverse the action of Heparin. It is eliminated through liver

     Low molecular weight heparin (LMWH) includes Enoxaparin and Deltaparin, also have the same action as of UF heparin, but it is eliminated renally. Fondaparinux is also an anticoagulant that is very similar to LMWH. Difference is that it has high specificity to Antithrombin-III.

2) Direct Thrombin Inhibitors: This includes the drugs Argatroban, Dabigatran, and Bivalirudin. If the patient is presented with Heparin-Induced Thrombocytopenia (HIT).

3) Direct Factor-Xa Inhibitors: This category includes drugs named Apixaban and Rivaroxaban. These are medicated orally and, used for long-term treatment of Atrial Fibrillation.

4)Warfarin: This is the only drug that is used to inhibit the Epoxide reductase enzyme to prevent the formation of Activated Vitamin-K. Vitamin-K is the major factor that helps in the activation of clotting factors. It is administered Orally and used for long-term anticoagulation treatment.

5) Cyclo-Oxygenase Inhibitors: This includes the drug named Aspirin, which inhibits Cox by doing its Acetylation, which leads to the irreversible inhibition of Cox so that Thromboxane-A2 is not formed.

6) P2Y12 Receptor Inhibitor: Drugs included in this category are Ticlopidine, Clopidogrel. Prasugrel, and Ticagrelor. As the ADP binds with the P2Y12 receptor of the platelet to cause its aggregation. These drugs inhibit aggregation by binding with that P2Y12 receptor so that ADP can not bind. 

7) Glycoprotein IIb/IIIa Receptor: Drugs in this category are Abciximab, Eptifibatide, and Tirofiban. Normally fibrinogen binds with Glycoprotein IIb/IIIa and helps in promoting aggregation. But to prevent blood clotting, these drugs are used that block the Glycoprotein IIb/IIIa receptor, so that fibrinogen can not bind there. During its therapy, the platelet count should be monitored.

8) Phosphodiesterase Inhibitors: The drugs that inhibit phosphodiesterase are Dipyridamol and Cilostazol. As the phosphodiesterase is inhibited, it leads to an increase in cAMP, which activates the Protein Kinase so platelet impairment occurs.

9) Anti-Thrombolytic drugs: As normally, for lysis of clot, endothelial cells secrete a tissue factor that is tissue Plasminogen Activator (tPA), that converts plasminogen to plasmin for lysis of the clot. But if that tPA is not secreted then the recombinant forms of tPA is given that are Reteplase, Tenecteplase, and Alteplase. Streptokinase is also an Anti-Thrombolytic drug, but it is antigenic so may cause an allergic reaction. For reversing its effects, Aminocaproic acid and Tranexamic acid are used.

Conclusion

     The above given all are the agents that prevent clotting of blood by different mechanisms. These drugs may cause any adverse effect, that depends on the patient and the dosage given by a physician. So, then use of that drug should be stopped, or a reversal agent should be given.