Anti-coagulants
Anticoagulants:
An anticoagulant is a pharmaceutical substance that prevents coagulation. They are used both in vivo as a medication for thrombotic disorders. Some chemical compounds are also used in vitro, in medical equipment, such as test tubes, blood transfusion bags and renal dialysis equipment.
They may be classified into:
- Used in VIVO
Injectable
Heparin and derivatives Oral
Vitamin K antagonists- Coumarin derivate: Warfarin & Acenocoumarol
- Indandione derivate: Phenindione
- Used in vitro
- Heparin - green bulb/ vacutainer
- Calcium complexing agents:
- Citrate - blue bulb (for collecting blood for prothrombin time) / vacutainer and blood transfusion bags.
- Oxalate - fluoride bulb/ vacutainer
- EDTA - lavender coloured bulb/ vacutainer
Dose regulation: The dose of oral anticoagulant must be individualized by repeated measurement of prothrombin time (PT); the aim is to achieve a therapeutic effect without unduly increasing the chances of bleeding.
The optimum ratio of PT during treatment to the normal value (of the testing laboratory) has been defined. A standardized system called International Normalized Ratio (INR) based on the use of human brain thromboplastin has been developed by WHO and adopted in all countries.
| 1) Prophylaxis of deep vein thrombosis and similar indications | INR 2-2.5 |
| 2) Treatment of deep vein thrombosis, pulmonary embolism, TIAs, hip surgery | INR 2-3 |
| 3) Recurrent thrombo-embolism, arterial disease, (MI) prosthetic heart valves | INR 3-4.5 |
Factors enhancing effect of oral anticoagulants are:
- Supply of Vit K to liver is reduced
- Debility,
- Malnutrition,
- Malabsorbtion and
- Prolonged antibiotic therapy
- Synthesis of clotting factors may be deficient
- Chronic liver disease
- Chronic alcoholism
- Clotting factors are degraded faster
- Hyperthyroidism
Factors decreasing effect of oral anticoagulants are:
- Pregnancy: plasma level of clotting factors is higher.
- Nephrotic syndrome: drug bound to plasma protein is lost in urine.
- Genetic warfarin resistance.
Fibrinolytics:
These are drugs used to lyse/ thrombin clot to recanalyse occulted blood vessels (mainly coronary artery). They are curative rather than prophylactic, work by activating the natural fibrinolytic system. In general venous thrombi are lysed more easily than arterial and recent thrombi respond better: little effect on thrombi> 3 days old.
Three fibrinolytics - Streptokinase, Urokinase and rTPA (recombinant tissue Plasminogen activator) are available in India for clinical use.
Antifibrinolytics: These are drugs which inhibit plasminogen activation and dissolution of clot.
- Epsilon amino- caproic acid (EACA): It is a specific antidote for fibrinolytic agents and has been used in many hyperplasminemic states associated with excessive intravascular fibrinolysis resulting in bleeding.
- Tranexaemic acid: 7 times more potent than EACA.