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.
|
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))
where:
• 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.
