Heparin

Drug Information: Heparin

Heparin is an anticoagulant medication widely used in clinical settings to prevent and treat thromboembolic disorders. It is a naturally occurring glycosaminoglycan that exerts its anticoagulant effects by activating antithrombin III, a plasma protein that inhibits several clotting factors. This action prevents the formation of blood clots and helps to manage conditions associated with Acute Coronary Syndrome (ACS) and other thrombotic events. Heparin is typically administered intravenously or subcutaneously.

Category

Drugs for ACS

Mechanism of Action

Heparin’s primary mechanism of action involves enhancing the activity of antithrombin III (AT-III), a naturally occurring anticoagulant in plasma. AT-III inhibits several serine proteases involved in the coagulation cascade, most notably thrombin (factor IIa) and factor Xa. Heparin binds to AT-III, causing a conformational change that dramatically accelerates the rate at which AT-III inactivates these clotting factors. Specifically, the heparin-AT-III complex binds to and neutralizes thrombin and factor Xa more effectively than AT-III alone. This results in the prevention of fibrin formation, which is essential for blood clot formation. The pentasaccharide sequence of heparin is responsible for its binding to AT-III. Once AT-III has bound to and inactivated a clotting factor, heparin can dissociate and bind to another AT-III molecule, allowing it to act catalytically. In essence, heparin acts as a cofactor to significantly boost the anticoagulant activity of AT-III, thereby preventing thrombus propagation and promoting thrombolysis.

Clinical Uses

Heparin is widely used in various clinical scenarios due to its anticoagulant properties. In the context of Acute Coronary Syndrome (ACS), it is administered to prevent further thrombus formation in patients experiencing unstable angina or myocardial infarction. It’s often used in conjunction with antiplatelet agents like aspirin and clopidogrel. Beyond ACS, Heparin is also indicated for the prophylaxis and treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE). It is employed during and after certain surgical procedures, particularly orthopedic and vascular surgeries, to prevent postoperative thrombotic complications. Furthermore, heparin is used in the management of disseminated intravascular coagulation (DIC) and during hemodialysis to prevent clotting within the dialysis circuit. In pregnant women, heparin is often preferred over oral anticoagulants like warfarin due to its lower risk of fetal harm. The versatility of heparin makes it a crucial medication in managing and preventing thromboembolic events in a variety of patient populations.

Dosage

Adult Dosage:
Prophylaxis of DVT/PE: 5,000 units subcutaneously every 8-12 hours.
Treatment of DVT/PE: Initial IV bolus of 80 units/kg, followed by continuous IV infusion of 18 units/kg/hour. Adjust infusion rate based on aPTT (activated partial thromboplastin time).
ACS (Unstable Angina/NSTEMI): Initial IV bolus of 60-70 units/kg (max 5,000 units), followed by continuous IV infusion of 12-15 units/kg/hour (max 1,000 units/hour). Adjust infusion rate based on aPTT.

Pediatric Dosage: Dosing varies greatly by indication and age. Consultation with a pediatric hematologist or pharmacist is crucial. Typical dosing requires weight-based calculations and close monitoring of aPTT.

Route of Administration: Heparin is administered either intravenously (IV) or subcutaneously (SC). IV administration is preferred for acute treatment, while SC administration is often used for prophylaxis.

Indications

Common indications for Heparin use include:
* Treatment and prophylaxis of venous thromboembolism (DVT and PE)
* Management of acute coronary syndromes (unstable angina, NSTEMI, STEMI)
* Anticoagulation during cardiopulmonary bypass and hemodialysis
* Prophylaxis of thromboembolism in high-risk surgical patients
* Treatment of arterial thromboembolism
* Prevention of clotting in arterial and cardiac surgery.

Contraindications

Contraindications for Heparin use include:
* Known hypersensitivity to heparin or heparin products
* Active major bleeding
* Severe thrombocytopenia (low platelet count)
* Uncontrolled hypertension
* Recent surgery of the brain, spinal cord, or eye
* Severe liver disease
* Hemophilia or other bleeding disorders
* History of Heparin Induced Thrombocytopenia (HIT)

FAQ

Q: What is Heparin used for?
A: Heparin is an anticoagulant used to prevent and treat blood clots in conditions like deep vein thrombosis, pulmonary embolism, and acute coronary syndromes.

Q: How is Heparin administered?
A: Heparin is usually administered intravenously (IV) or subcutaneously (SC).

Q: What are the common side effects of Heparin?
A: Common side effects include bleeding, thrombocytopenia (low platelet count), and injection site reactions.

Q: What is Heparin-Induced Thrombocytopenia (HIT)?
A: HIT is a serious complication where heparin paradoxically causes a decrease in platelets and an increased risk of thrombosis.

Q: How is Heparin’s effectiveness monitored?
A: Heparin’s effectiveness is monitored by measuring the activated partial thromboplastin time (aPTT).

Q: Can Heparin be used during pregnancy?
A: Yes, Heparin is often preferred over warfarin during pregnancy due to its lower risk of fetal harm, but should only be taken when neccessary after consulting a doctor.

Q: What is the antidote for Heparin overdose?
A: Protamine sulfate is the antidote for Heparin overdose. It binds to heparin and neutralizes its anticoagulant effect.

Q: What should I tell my doctor before starting Heparin?
A: Inform your doctor about any allergies, bleeding disorders, recent surgeries, and all other medications you are taking, including over-the-counter drugs and herbal supplements.