Heparin (unfractionated)


Unfractionated heparin is an anticoagulant that activates antithrombin III which in turn inactivates thrombin and factor Xa to produce its effect. Frequently referred to simply as “heparin”, this drug is infused intravenously for an almost immediate onset of action and has a variable response necessitating close monitoring with the activated partial thromboplastin time (aPTT). The therapeutic aPTT is variable depending on the reagent used to perform the testing and thus “heparin nomograms” are available at each institution to guide dosing adjustment.


Acute coronary syndromes, atrial fibrillation, venothromboembolism (VTE), cardiopulmonary bypass, coating on multiple medical devices.

Adverse Effects

Bleeding, heparin induced thrombocytopenia (HIT), elevated liver function testing, aldosterone inhibitory effect causing hyperkalemia


Protamine sulfate is considered the antidote to reverse the effects of heparin.

Rarely heparin resistance can occur in the setting of antithrombin III deficiency.

Low-molecular weight heparin should not be confused with unfractionated heparin.