From the Guidelines
Clexane (enoxaparin) is a low molecular weight heparin that primarily inhibits factor Xa with minimal effect on thrombin (factor IIa), whereas Unfractionated Heparin (UFH) binds to antithrombin and inhibits multiple coagulation factors including thrombin and factor Xa. The mechanism of action of these two anticoagulants differs significantly, with enoxaparin having a more predictable anticoagulant response due to its balanced anti-Xa and anti-IIa activity 1. Enoxaparin is readily absorbed after subcutaneous administration and has less platelet activation, which reduces the risk of heparin-induced thrombocytopenia. In contrast, UFH requires more frequent monitoring via activated partial thromboplastin time (aPTT) due to its unpredictable anticoagulant response. Some key points to consider when choosing between enoxaparin and UFH include:
- Enoxaparin has a longer half-life (4-6 hours) allowing for once or twice daily dosing, typically 1mg/kg twice daily or 1.5mg/kg once daily for therapeutic anticoagulation 1.
- UFH is administered as a continuous infusion (starting at 18 units/kg/hour) after an initial bolus (80 units/kg) with dose adjustments based on aPTT results.
- Enoxaparin offers advantages including more predictable pharmacokinetics, less monitoring, reduced risk of heparin-induced thrombocytopenia, and lower incidence of osteoporosis with long-term use 1.
- However, UFH may be preferred in patients with severe renal impairment (as enoxaparin is renally cleared) or when rapid reversal of anticoagulation might be needed, as protamine sulfate completely reverses UFH but only partially neutralizes enoxaparin. Overall, enoxaparin is a preferred choice over UFH due to its predictable anticoagulant response, reduced risk of heparin-induced thrombocytopenia, and lower incidence of osteoporosis with long-term use 1.
From the Research
Mechanism of Action of Clexane (Enoxaparin) versus Unfractionated Heparin (UFH)
The mechanism of action of Clexane (enoxaparin) and Unfractionated Heparin (UFH) can be understood by examining their effects on the coagulation pathway. Key points include:
- Enoxaparin has a higher ratio of anti-Xa to anti-IIa activity (3:1) compared to UFH, which may contribute to its therapeutic benefits 2
- Enoxaparin has a more predictable dose response and does not require frequent monitoring, unlike UFH which requires routine monitoring of the activated partial thromboplastin time (aPTT) to ensure adequate levels of anticoagulation are maintained 3
- The anti-Xa activity of enoxaparin is more stable and predictable, which may reduce the risk of rebound thrombosis and contribute to its superiority over UFH 4
Comparison of Enoxaparin and UFH in Clinical Settings
Studies have compared the efficacy and safety of enoxaparin and UFH in various clinical settings, including:
- Acute coronary syndromes: enoxaparin has been shown to reduce the rate of deaths and serious cardiac events compared to UFH 5, 3
- Venous thromboembolism: enoxaparin has been shown to be effective in preventing venous thromboembolism, with similar efficacy and safety to UFH 5, 6
- Cancer, orthopedic, or vascular surgery: enoxaparin has been shown to be more effective than UFH in preventing venous thromboembolism, with similar rates of bleeding complications 5
Monitoring of Anticoagulation
The monitoring of anticoagulation with enoxaparin and UFH differs:
- UFH requires routine monitoring of aPTT to ensure adequate levels of anticoagulation are maintained 3
- Enoxaparin does not require frequent monitoring, as its anti-Xa activity is more stable and predictable 2
- Activated clotting time (ACT) is not useful for assessing anticoagulation with subcutaneous enoxaparin and should not be relied on in patients receiving enoxaparin who require acute percutaneous coronary intervention (PCI) 2