Cardiovascular Drugs and Medications Q 54
The half-life of heparin is:
A. 10 minutes
B. 1 to 1.5 hours
C. 8 to 12 hours
D. 1 to 2 days
Correct Answer: B. 1 to 1.5 hours
The half-life of heparin is 60 to 90 minutes. This is important to know when bleeding occurs during heparin administration. Once administered, heparin binds to several proteins; however, it is binding to antithrombin that is important, as this causes a surface change and inactivates thrombin. By binding to antithrombin, it blocks several different factors of the clotting cascade, but two are predominant: thrombin (Factor IIa) and Factor Xa. By inactivating thrombin, it blocks the conversion of fibrinogen to fibrin; this prevents the formation of clots and prolongs the clotting time of blood. Heparin does not affect bleeding time, but it does prolong the time that blood takes to clot.
Option A: Therapeutic monitoring for heparin includes activated partial thromboplastin time (aPTT) and activated clotting time (ACT). Both of these are aspects of clotting time, which are prolonged by therapeutic heparin doses. Activated partial thromboplastin time is performed at baseline and every 6 hours until 2 or more therapeutic values are obtained, then aPTT can be assessed every 24 hours. Dose titrations are made based on the results of the aPTT.
Option C: Typical adverse effects from heparin use include bleeding, thrombocytopenia, injection site reactions, and other adverse effects only seen with chronic heparin administration. Bleeding is a major complication associated with heparin use. Patients should undergo monitoring for new bleeding that may present in the urine or stool. Bleeding may also present as bruising, petechial rash, and nosebleeds.
Option D: Heparin administration can be by intravenous (IV) route or subcutaneous SQ) route. Intravenous heparin is continuously administered for therapeutic anticoagulation, while intermittent subcutaneous administration is used to prevent thromboembolism. Intermittent IV administration is also an option. When administered SQ, the onset of action is usually within 1 to 2 hours as compared to an immediate anticoagulant effect with IV administration of heparin.