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| Heparin calcium |
Heparin calcium is one of the most widely used anticoagulant or blood thinner medications used today. Let us take a deeper look at this important drug in this article.
What is Heparin Calcium?
Heparin calcium is a naturally occurring molecule commonly obtained from mammalian tissues such as lungs or intestinal mucosa. It is commonly provided as the calcium salt form which is known as heparin calcium. Chemically, heparin calcium is a glycosaminoglycan polymer composed of alternating residues of D-glucosamine and uronic acid.
Mechanism of Action
Heparin calcium works by inhibiting several clotting factors involved in the blood coagulation cascade. Specifically, it acts by binding to and facilitating the actions of antithrombin III, a naturally present protein in our blood that inactivates coagulation factors such as thrombin (factor IIa) and factor Xa. By binding to antithrombin III, heparin calcium increases its inhibitory actions against thrombin and factor Xa by about a thousand-fold. This prevents the excessive production of fibrin clots within blood vessels.
Medical Uses
As an anticoagulant, heparin calcium has various important medical uses:
- Treatment of deep vein thrombosis and pulmonary embolism: By preventing further clot formation, heparin calcium is commonly used to treat existing blood clots in the legs (deep vein thrombosis) or lungs (pulmonary embolism).
- Prevention of clots during surgery or medical procedures: Heparin calcium is routinely given before and after surgeries or medical procedures like coronary bypass, angioplasty and dialysis to reduce the risk of blood clots forming during or after these interventions.
- Treatment of heart attacks: Low molecular weight heparins like enoxaparin are often used in patients with heart attacks to prevent recurrent clot formation and further heart damage.
- Treatment of unstable angina: Heparin helps reduce angina attacks and the risk of heart attacks in patients with unstable angina by preventing coronary arterial clots.
Route of Administration and Dosing
Heparin calcium is usually given by intravenous (IV) injection or continuous IV infusion to attain its quick onset of action. It has a very short biological half-life of about 60 minutes.
The standard initiation dose is 80 units/kg body weight given as an IV bolus followed by 18 units/kg/hour as a continuous IV infusion. Dosage adjustments are made based on regular monitoring of anti-factor Xa levels or activated partial thromboplastin time (aPTT), which are measures of heparin's anticoagulant effect. Therapeutic aPTT ranges are typically 1.5 to 2.5 times higher than normal levels.
Adverse Effects and Monitoring
Like all potent anticoagulants, heparin calcium too increases the risk of bleeding complications like hematoma, blood in urine or stool. Other common side effects include injection site pain, nausea, diarrhea and elevated liver enzymes.
Due to the risk of bleeding, patients on heparin therapy undergo regular monitoring of hemoglobin levels and frequently check for signs of internal or external bleeding. Platelet counts are also monitored as heparin can cause a mild reduction in platelet levels.
As heparin's effect and half-life is highly variable between individuals, regular aPTT or anti-Xa level monitoring is mandatory to maintain heparin levels within the therapeutic window and prevent under or over-anticoagulation. Protamine sulfate is used to rapidly reverse the effects of heparin in case of major bleeding events.
Heparin-Induced Thrombocytopenia (HIT)
A serious albeit rare adverse effect associated with heparin use is immune-mediated heparin-induced thrombocytopenia (HIT). In HIT, antibodies develop against the heparin-PF4 complex which leads to platelet activation and paradoxical thrombosis. Diagnosis of HIT warrants immediate discontinuation of heparin and use of alternative anticoagulants like argatroban or danaparoid. HIT can progress to life-threatening conditions like deep vein thrombosis if unrecognized.
Low Molecular Weight Heparins
Research led to the development of low molecular weight heparins derived from heparin calcium through depolymerization, with molecules of average lower size (5000-8000 Da). These include enoxaparin, dalteparin, tinzaparin etc.
Low molecular weight heparins have advantages over unfractionated heparin calcium in having more predictable pharmacokinetics requiring less monitoring, longer half-life allowing once or twice daily dosing and a safer risk profile with reduction in HIT and bleeding risks. Hence, they are now preferred over heparin for most indications.
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