Anticoagulants and Its Types

• Anti-coagulants: Those substances that do not allow blood to coagulate by preventing or postponing it.
• Taken as medicines, given to the people who have high risk of getting clot.
• Minimize the chance of facing serious situations of heart attack and strokes.
• Also called blood thinners.
• Are of three types:

A) Anticoagulants in blood clotting prevention inside the body.

i.e., in vivo

B) Anticoagulants preventing the clotting of blood collected from the body.

i.e., in vitro

C) Anticoagulants preventing blood clotting both in vitro and in vivo.

Heparin

• Anticoagulant produced naturally inside body.
• Wandering cells called mast cells produces it.
• Mast cells are present immediately outside the capillaries.
• Mast cells are present in many tissues or organs containing more connective tissue.
• Abundant in liver and lungs.
• Basophils also produce heparin.
• A conjugated poly-saccharide which are produced from organs and liver of animals.
• Done for commercial purpose.
• Available in liquid form or dry form in commercial preparation.
• In dry form as sodium, calcium, ammonium or lithium salts.

Image source: orthobullets

Mechanism of action

• Has anti-thrombin activity that suppresses the activity of thrombin directly.
• Heparin combines with anti-thrombin III.
• Anti-thrombin III is a protease inhibitor present in blood circulation.
• Thus, this combination removes thrombin from
• Heparin not only combines but also activates anti-thrombin III.
• Active form of other clotting factors gets inactivated.

Uses of Heparin

• In both in vivo and in vitro, used as an anticoagulant.
• Intravenous injection of heparin prevents or postpones clotting.
• Clotting is prevented for 3-4 hours.
• The dose use is 5-1 mg/kg body weight.
• Acts or works unless it gets damaged by enzyme
• In clinical practice, this method is generally used.
• Besides that, for other purposes also heparin is used in clinics.
• They are:

1. During surgery to prevent intravascular clotting.
2. During dialysis when blood is passed through artificial kidney.
3. Cardiac surgery which uses heart-lung machine also uses heparin.
4. Before transfusing the blood, the blood is preserved using heparin.

• Blood collected for investigations purpose in vitro also uses heparin as anticoagulant.
• For 1 ml of blood, the dose is 0.1-0.2 mg.
• Works for 8-12 hours after which clotting cannot be prevented.
• Only clotting is delayed not prevented by heparin.
• Most expensive anticoagulant.

 Image source: researchgate

Coumarin Derivatives

• Warfarin and di-coumoral falls under this group.
• Vitamin K activity inhibited by these derivatives.
• Various clotting factors formation requires vitamin K.
• As, activity of vitamin k is prevented, clotting factors are not formed.
• Thus, clotting is prevented with inhibited activity of vitamin K.
• Clotting factors like II, VII, IX and X requires vitamin K for formation.
• Warfarin and dicoumoral are oral anticoagulants.
• Heart attack(myocardial infarction), strokes and thrombosis are prevented by warfarin.

EDTA

• Short form of ethylenediaminetetraacetic acid.
• A strong anticoagulant available in two forms.
• Disodium salt (Na₂EDTA) and tri-potassium salt (K₃EDTA).
• Removes calcium from blood for preventing blood clotting.
• Used in both in vivo and in vitro.
• In case of lead poisoning, administered intravenously.
• For preserving blood for at least 6 hours in laboratory EDTA is used.
• Requirement is 0.5- 2.0 mg of EDTA per ml blood.
• Blood is preserved for long period about 24 hours on refrigeration with EDTA.

Oxalates Compounds

• Leads to formation of calcium oxalate thus preventing coagulation.
• This gets precipitated later on after sometime.
• Blood calcium level gets reduced by these compounds affect.
• Before, sodium and potassium oxalates were used.
• At present, mixture of ammonium oxalate and potassium oxalate is used in ratio of 3:2.
• Each salt is individually anti-coagulant in nature.
• When used alone, potassium oxalate shrinks RBCs.
• Likewise, alone use of ammonium oxalate causes RBCs swelling.
• Thus, for normal cellular activity they are used in combined form.

Mechanism of Action

• Oxalate combines with calcium, form insoluble calcium oxalates.
• This activity decreases calcium level in blood.
• In turn, coagulation is prevented in lack of calcium.

Uses of oxalate compounds

• Used only for in vitro
• For 1 ml of blood, 2 mg of mixture of these compounds required.
• In vivo, its use is not practiced as it is poisonous.

Other anticoagulants

• Hirudin, C-type lectin and peptone are known other anticoagulants.
• Hirudin is obtained from the leach Hirudinaria manillensis.
• Peptone and C-type lectin are the proteins from venom of viper snake.

References: 

i) https://www.webmd.com/dvt/anticoagulant-types

ii) https://www.drugs.com/drug-class/anticoagulants.html

iii) https://www.healio.com/news/cardiology/20220114/frail-patients-less-likely-to-receive-certain-blood-thinners-despite-recommendations

Anticoagulants and Its Types