In the event of heparin overdosage it may be necessary to reverse the heparinization to prevent severe hemorrhage. Protamine sulfate can be used for this purpose, with 1 milligram of protamine sulfate capable of reversing the effect of 100 units of heparin.


NOTE: Protamine sulfate will reverse unfractionated heparin but not low molecular weight formulations.


If we assume 1st order kinetics, 4-5 half-lives will eliminate almost all of the heparin in the patient.


Heparin half-life is dose-dependent and increases with dose.



Heparin Half-Life

25 IU/kg

30 minutes

100 IU/kg

60 minutes

400 IU/kg

150 minutes


An equation approximating this:


heparin half-life in hours =

= ((heparin dose in IU per kg) * 0.005238) + 0.41667


With first order kinetics:


(amount of heparin in the body at time T) =

= (original dose of heparin) * (e^((-1) * k * T))



• k = ((0.693) / (half-life))


From the original dose and time, the number of units of heparin present at a given time can be calculated. This amount divided by 100 will give the number of milligrams of protamine sulfate to administer.


Excess protamine sulfate should be kept to a minimum, since it will have an anticoagulant effect.


NOTE: Need to determine if actual body weight or ideal body weight should be used for calculations.


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