enoxaparin

Enoxaparin binds antithrombin III via a pentasaccharide sequence, accelerating its inhibition of Factor Xa much more than thrombin (Factor IIa), giving it a higher anti-Xa:anti-IIa ratio (~3-4:1) compared to unfractionated heparin (1:1). This selective Xa inhibition provides more predictable dose-response, allowing weight-based subcutaneous dosing without routine coagulation monitoring (unlike UFH, which requires aPTT monitoring due to variable protein/cell binding).

Clinical uses include: prophylaxis and treatment of DVT/PE, bridging anticoagulation (e.g., around warfarin initiation or discontinuation for surgery), and as adjunct therapy in ACS (NSTEMI/STEMI) and during PCI.

Pharmacokinetics: administered subcutaneously, has longer half-life than UFH allowing once or twice daily dosing, and is renally cleared—requiring dose adjustment in renal impairment (CrCl <30 mL/min) due to risk of accumulation and bleeding.

Monitoring: routine monitoring is not required, but anti-Xa levels can be checked in special populations (renal impairment, obesity, pregnancy).

Adverse effects: bleeding is the primary risk. Heparin-induced thrombocytopenia (HIT) can occur but is less common than with UFH due to lower affinity for platelet factor 4. Enoxaparin can also cause hyperkalemia (via aldosterone suppression) and osteoporosis with long-term use.

Reversal: Protamine sulfate partially reverses enoxaparin's anticoagulant effect (only neutralizes ~60% of anti-Xa activity, more effective against anti-IIa activity) compared to complete reversal of UFH.

Contraindications/cautions: active major bleeding, severe renal impairment (dose reduce), history of HIT (cross-reactivity possible), neuraxial anesthesia (risk of spinal/epidural hematoma—timing must be carefully managed).

Key boards point: LMWH vs. UFH—LMWH has more predictable dosing, longer half-life, lower HIT risk, but reversal is incomplete and requires renal dose adjustment; UFH is preferred in renal failure, when rapid reversal may be needed, or in patients requiring precise titration (e.g., cardiac surgery, dialysis).