Anticoagulants are medicines that help prevent unwanted blood clots. Blood normally clots to stop bleeding, but sometimes clots form inside blood vessels, blocking blood flow. This can cause serious problems like heart attack, stroke, or deep vein thrombosis (DVT). Anticoagulants reduce the blood’s ability to clot and help keep blood vessels open.
Types of Anticoagulants
Anticoagulants are mainly divided into two groups based on how they are given:
1. Parenteral (Injectable) Anticoagulants
These medicines are given through a vein or under the skin. They work quickly and are commonly used in emergency or hospital settings. The major injectable anticoagulants include:
a. Unfractionated Heparin (UFH)
Heparin is one of the oldest and most commonly used anticoagulants. It is obtained from animal tissues and is strongly acidic in nature. Because it is not absorbed through the stomach, it must be given either through an IV (for immediate action) or through a subcutaneous injection.
Mechanism of Action
- Heparin binds to a natural protein in the blood called antithrombin III.
- This combination becomes very active and blocks several clotting factors, especially factor Xa and thrombin (factor IIa).
- As a result, the blood takes longer to clot and prevents new clots from forming.
Key Features
- Works immediately when given through IV.
- Does not cross the placenta—safe for pregnancy.
- Needs regular blood test monitoring called aPTT to ensure correct dosing.
Adverse Effects
- Bleeding – most important risk. Severe bleeding can be reversed using protamine sulphate.
- Heparin-Induced Thrombocytopenia (HIT) – a rare but serious drop in platelets caused by the immune system.
- Allergic reactions, hair loss, osteoporosis (in long-term use).
Contraindications
Heparin should not be used in patients with conditions like active bleeding, haemophilia, severe hypertension, peptic ulcers, or recent surgeries involving the brain or spinal cord.
2. Low Molecular Weight Heparins (LMWHs)
Examples: Enoxaparin, Dalteparin, Tinzaparin
LMWHs are smaller fragments of heparin. They act mainly by blocking factor Xa and have minimal effect on thrombin.
Advantages Over Regular Heparin
- More predictable effect, so no routine monitoring is needed.
- Given once daily due to longer half-life.
- Lower risk of HIT and osteoporosis.
- Better absorption when given under the skin.
Limitations
Their effect is only partially reversed by protamine sulphate. They must still be used carefully in kidney disease.
3. Fondaparinux
Fondaparinux is a synthetic anticoagulant given under the skin. It works by selectively blocking factor Xa through antithrombin, with no direct effect on thrombin.
Key Points
- Used in DVT and pulmonary embolism.
- Long half-life (about 17 hours) allows once-daily dosing.
- Lower risk of HIT and osteoporosis compared to heparin.
Pharmacokinetics of Heparin
- Absorption: Not absorbed orally, must be injected.
- Distribution: Does not cross the placenta or enter the brain.
- Metabolism: Broken down in the liver.
- Excretion: Metabolites leave through urine.
Administration & Monitoring
Heparin is usually given as an IV infusion for rapid effect or as a subcutaneous injection for prevention purposes. The aPTT level must be kept 1.5–2.5 times the normal value to ensure safe anticoagulation.
The intramuscular route is avoided because it can cause painful blood clots under the skin.
Antidote for Heparin
Protamine sulphate is the specific antidote used to reverse heparin’s effect in case of severe bleeding.
- 1 mg of protamine neutralizes 100 units of heparin.
- The maximum safe dose is 50 mg.
Uses of Anticoagulants
Anticoagulants are used in many clot-related conditions:
- Deep vein thrombosis (DVT)
- Pulmonary embolism
- Heart attack (as supportive therapy)
- During major surgeries to prevent clot formation
- In certain heart rhythm problems like atrial fibrillation
Detailed Notes:
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