LMWH

Low molecular weight heparin (LMWH) is a class of anticoagulants derived from standard heparin by controlled depolymerization, producing shorter polysaccharide chains. The main LMWH products include enoxaparin, dalteparin, and tinzaparin. LMWHs offer more predictable pharmacokinetics and a lower risk of certain complications compared with unfractionated heparin (UFH), allowing for fixed, weight-based dosing and subcutaneous administration.

Mechanism and pharmacokinetics: LMWHs accelerate the activity of antithrombin III, with preferential inhibition of factor Xa and lesser inhibition of thrombin (factor IIa) than UFH. This reduces thrombin generation and clot formation. Their shorter chains yield more predictable anticoagulant responses and a longer half-life, which supports outpatient use and simplified dosing without routine coagulation monitoring in most patients. They are primarily cleared by the kidneys, so renal function influences dosing.

Indications and administration: LMWHs are used for prevention of venous thromboembolism after many surgeries and in acutely ill medical patients, as well as for the treatment of acute DVT and/or pulmonary embolism. They are also used as bridging therapy around transitions to or from other anticoagulants. Administration is by subcutaneous injection, often in a hospital setting, with some regimens suitable for home use.

Monitoring, safety, and contraindications: Routine coagulation monitoring is not required, but anti-Xa activity may be checked in selected populations (e.g., very high or low body weight, pregnancy, renal impairment, pediatrics). Common adverse effects include bleeding and injection-site reactions; heparin-induced thrombocytopenia is less common than with UFH but warrants vigilance. Cautions include active major bleeding, severe renal impairment, and history of HIT. Reversal with protamine sulfate partially neutralizes LMWH activity.

Examples: enoxaparin (Lovenox, Clexane) and dalteparin (Fragmin).