Heparins and oral anticoagulants Flashcards
Example of a heparin & oral anticoagulants
Tissue plasminogen activator & enoxaparin
How do heparins work?
Thrombin and factor Xa are key components of the final common coagulation pathway that leads to formation of a fibrin clot. By inhibiting their function, heparins and fondaparinux prevent the formation and propagation of blood clots.
Unfractionated heparin (UFH) activates antithrombin that, in turn, inactivates clotting factor Xa and thrombin.
Low molecular weight heparins such as dalteparin and enoxaparin have a similar mechanism of action but preferentially inhibit factor Xa. Low molecular weight heparins have a more predictable effect and, unlike UFH, do not usually require laboratory monitoring. Consequently, LMWHs are now preferred in most indications.
Indications for heparin
Venous thromboembolism (VTE): low molecular weight heparin (LMWH) is the first choice agent for pharmacological VTE prophylaxis in hospital inpatients, and for initial treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE).
Acute coronary syndrome (ACS): LMWH or fondaparinux are part of first-line therapy to improve revascularisation and prevent intracoronary thrombus progression.
Contraindications of heparin
Anticoagulants should be used with caution in patients at increased risk of bleeding, including those with clotting disorders, severe uncontrolled hypertension, or recent surgery or trauma.
Heparins should be avoided around the time of invasive procedures, particularly lumbar puncture and spinal anaesthesia. In patients with renal impairment,
LMWH and fondaparinux may accumulate and should be used at a lower dose, or unfractionated heparin used instead.
Side effects of heparin
Main: Bleeding, Injection site reactions
Rare & dangerous: heparin-induced thrombocytopenia (low platelet count and thrombosis
Interactions of heparin
Combining antithrombotic drugs increases the risk of bleeding. This should usually be avoided unless there is a special reason for combined therapy, such as in the use of LMWH while initiating warfarin, or the use of antiplatelet drugs (e.g. aspirin, clopidogrel) with fondaparinux/LMWH in ACS.
In major bleeding associated with heparin therapy, protamine can be given to reverse anticoagulation. This is effective for UFH but much less so for LMWH. It is ineffective against fondaparinux.
Elimination of heparin
Heparin is removed from the blood via two mechanisms, saturable and non-saturable. The saturable mechanism represents clearance by the reticuloendothelial system and endothelial cells, to which heparin binds with a high affinity. The non-saturable mechanism is represented by renal excretion.
Patient information on heparin
SC injections of these drugs should be given into the subcutaneous tissue of the abdominal wall. The arm should not be used because this can cause uncomfortable and disabling bruising.
Explain that you are offering a daily injection that will reduce the risk of blood clots.
In longer-term therapy (e.g. for the treatment of VTE in cancer, when LMWH may be preferred over warfarin), discuss the risks and benefits of anticoagulation. Advise patients to avoid activities that may increase their risk of bleeding, such as contact sports, and to inform healthcare professionals they come into contact with that they are taking anticoagulants.
