1 Heparin and Low-Molecular-Weight Heparins

How heparins reduce clot formation

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) both reduce clot formation by enhancing antithrombin’s inhibition of activated clotting factors.

UFH has substantial activity against thrombin (factor IIa) and factor Xa. LMWHs, including enoxaparin, have proportionally greater anti-Xa than anti-IIa activity.

Uses and choosing between heparins

Heparin products may be used to prevent venous thromboembolism in at-risk hospitalized or postoperative patients, or to treat deep-vein thrombosis and pulmonary embolism. UFH also has uses in settings such as dialysis and procedures where anticoagulation is required.

UFH may be preferred when rapid adjustment or stopping of anticoagulation is important, or when severe renal impairment makes LMWH accumulation a concern. Selection also depends on the clinical setting, bleeding risk, and treatment protocol.

Dosing and patient factors

Before giving an LMWH dose, confirm the indication, prescribed regimen, body weight when relevant, kidney function, bleeding risk, and the correct product and concentration.

Prophylaxis and treatment use different dosing strategies. Therapeutic regimens are commonly weight-based, while prophylactic regimens are often fixed-dose; the doses are not interchangeable. Severe renal impairment may require dose adjustment. Verify the applicable product labeling and protocol rather than extrapolating a dose.

Monitoring treatment

A therapeutic UFH infusion is commonly adjusted using the aPTT or an institution’s validated anti-Xa protocol. Routine aPTT or PT/INR testing does not reliably measure enoxaparin’s anticoagulant effect.

During heparin therapy, check blood counts, including platelet counts, and assess for bleeding. Anti-Xa testing may be considered in selected situations, such as renal impairment or a suspected abnormal response.

Bleeding, thrombocytopenia, and HIT

Important hazards of heparin therapy include bleeding and thrombocytopenia, including heparin-induced thrombocytopenia (HIT). Consider HIT if a patient receiving heparin has a substantial platelet-count fall and a new thrombosis. HIT can cause thrombosis despite a low platelet count.

If acute HIT is suspected or confirmed, stop heparin and initiate an appropriate non-heparin anticoagulant under clinical guidance. Do not simply switch from UFH to LMWH.

Administration safety checks

Before administration, verify the patient, drug, concentration, dose, and route. Use the prescribed weight-based or protocol-based regimen, and check for active bleeding, relevant platelet trends, kidney impairment when using LMWH, and concurrent drugs that increase bleeding risk.

Avoid intramuscular injection of UFH because of hematoma risk. Actual drug selection and dosing depend on the indication, patient factors, product labeling, and local protocol.

Reversal

Protamine sulfate reverses UFH. It can also be used for enoxaparin-associated bleeding, but reversal of LMWH is incomplete. Follow product-specific guidance and the urgent-care protocol.