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Heparins: Heparin and Low-Molecular-Weight Heparin
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Heparins: Heparin and Low-Molecular-Weight Heparin
Heparin
is a large molecule that is very acidic.
Enoxaparin
is an example of a low-molecular-weight (LMW) heparin with the same mechanism of action and use as
heparin
, but is smaller in molecular weight.
LMW heparin is longer acting when compared to
heparin
and can be dosed less frequently.
Heparins as a class cannot be absorbed by the gastrointestinal system, so they are administered intravenously or subcutaneously.
Heparins are safe in pregnancy.
Mechanism of action:
Heparin
and LMW heparin function is dependent on antithrombin III (ATIII), a component of the hemostasis system discussed earlier. ATIII normally inhibits factor IIa (thrombin) and factor Xa, thus causing anticoagulation. Heparins enhance the activity of ATIII, leading to very fast anticoagulation.
Use:
Heparins are used when the patient needs anticoagulated quickly (eg, deep vein thrombosis, myocardial infraction). They are also used in the hospital setting as deep vein thrombosis prophylaxis, as patients are often immobile and subjected to increased risk of deep vein thrombosis.
Laboratory measurement:
The aPTT test (measured in seconds) is used to monitor
heparin
and will be prolonged after the administration of heparin. An
aPTT result of 1.5x to 2.5x the reference range
is the goal. NOTE: LMW heparin is NOT monitored with the aPTT.
Toxicity:
Anticoagulants cause excessive bleeding if not dosed properly.
Protamine
is a basic molecule that can be used to neutralize the acidic
heparin
.
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