What Is Unfractionated Heparin?


Heparin is an anticoagulant used for the prevention and treatment of thrombosis, or blot clot formation. Unfractionated heparin (UFH) is a naturally occurring polysaccharide that works as an anticoagulant by inhibiting the activity of several blood coagulation factors.


  • UFH is primarily used for the acute treatment of thromboembolic disorders, a group of conditions characterized by the formation of blood clots (thrombus). UFH can also be used for the prevention of blood clot formation in high-risk patients.


  • UFH is often administered intravenously, though it may be given by other routes. It is never administered orally.

Mechanism of Action

  • UFH binds to antithrombin and enhances its activity. Antithrombin inhibits blood coagulation factors IXa, Xa, XIIa and thrombin (IIa). The inhibition of thrombin also prevents the activation of factors V and VIII. UFH prevents the growth of a blood clot, and also stimulates the body’s own clot-fighting system to destroy the thrombus.


  • UFH has an unpredictable anticoagulant response among patients, and requires close monitoring. Several blood tests are used to monitor the safety and effectiveness of UFH therapy, including whole clotting time, activated partial thromboplastin time, activated clotting time, anti-factor Xa activity and plasma heparin concentrations.

Adverse Drug Reactions

  • Bleeding is the most common adverse reaction associated with UFH. Thrombocytopenia, a decreased platelet count, is also associated with UFH therapy.

Related Compounds

  • Fractionated heparin, or low molecular weight heparin (LMWH), is a product of the breakdown of UFH. LMWH has a similar mechanism of action and use as UFH, but has more predictable anticoagulant activity among patients.

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  • DiPiro JP, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A pathophysiologic approach. 5th ed. New York, New York: McGraw-Hill; 2002.
  • Lacy CF, Armstrong LL, Goldman MP, Lance LL. Drug information handbook. 11th ed. Hudson, OH: Lexi-Comp; 2003.
  • Hirsh J, Anand SS, Halperin JL, Fuster V. Mechanism of action and pharmacology of unfractionated heparin. Arterioscler Thromb Vasc Biol. Jul 2001;21(7):1094-1096.
  • Photo Credit Ryan McVay/Photodisc/Getty Images
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