Unfractionated Heparin (IV)

How it works

It binds antithrombin and greatly accelerates its inactivation of thrombin and activated factor Xa, producing immediate anticoagulation that can be reversed with protamine.

Prescribing in practice

• Bleeding is the major hazard and the dose must be titrated to a coagulation target, with protamine available for reversal; avoid in active major bleeding and severe uncontrolled hypertension.
• Heparin-induced thrombocytopenia is a serious immune-mediated complication, so monitor the platelet count and stop heparin if it falls significantly or new thrombosis occurs.
• It can cause hyperkalaemia through aldosterone suppression, so check potassium in those at risk such as patients with diabetes or renal impairment, and weight-based nomograms guide infusion adjustment.

Monitoring

Monitor activated partial thromboplastin time (or anti-Xa) to titrate the infusion, with regular platelet counts for heparin-induced thrombocytopenia and potassium in at-risk patients.

Counselling the patient

• Explain this is a closely monitored drip that thins the blood and is adjusted by blood tests.
• Report any unusual bruising or bleeding promptly.
• Tell staff of any past reaction to heparin.

Evidence & guidelines

Its use across thromboembolic and procedural anticoagulation is long-established and supported by the SPC and NICE guidance, with monitoring and reversal advantages over low molecular weight heparins in selected patients.