indication

For the prophylaxis of deep vein thrombosis, which may lead to pulmonary embolism, and also for the prophylaxis of ischemic complications of unstable angina and non-Q-wave myocardial infarction, when concurrently administered with aspirin.

pharmacology

Enoxaparin is a highly acidic mucopolysaccharide formed of equal parts of sulfated D-glucosamine and D-glucuronic acid with sulfaminic bridges. The molecular weight ranges from 3800 to 5000 daltons. Enoxaparin occurs in and is obtained from liver, lung, mast cells, etc., of vertebrates. Enoxaparin is a well known and commonly used anticoagulant which has antithrombotic properties. Enoxaparin inhibits reactions that lead to the clotting of blood and the formation of fibrin clots both in vitro and in vivo. Enoxaparin acts at multiple sites in the normal coagulation system. Small amounts of enoxaparin in combination with antithrombin III (enoxaparin cofactor) can inhibit thrombosis by inactivating activated Factor X and inhibiting the conversion of prothrombin to thrombin. Once active thrombosis has developed, larger amounts of enoxaparin can inhibit further coagulation by inactivating thrombin and preventing the conversion of fibrinogen to fibrin. Enoxaparin also prevents the formation of a stable fibrin clot by inhibiting the activation of the fibrin stabilizing factor. Its use should be avoided in patients with a creatinine clearance less than 20mL/min. In these patients, unfractionated heparin should only be used. As for monitoring, active partial thromboplastin time (aPTT) will only increase at high doses of low molecular weight heparins (LMWH). Therefore, monitoring aPTT is not recommended. However, anti-Xa activity can be measured to monitor the efficacy of the LMWH.

mechanism of action

The mechanism of action of enoxaparin is antithrombin-dependent. It acts mainly by accelerating the rate of the neutralization of certain activated coagulation factors by antithrombin, but other mechanisms may also be involved. The antithrombotic effect of enoxaparin is well correlated to the inhibition of factor Xa. Enoxaparin interacts with Antithrombin III, Prothrombin and Factor X. Enoxaparin binds to and accelerates the activity of antithrombin III. By activating antithrombin III, enoxaparin preferentially potentiates the inhibition of coagulation factors Xa and IIa.

toxicity

Mouse, median lethal dose greater than 5000 mg/kg. Another side effect is heparin induced thrombocytopenia (HIT syndrome). HIT is caused by an immunological reaction that makes platelets form clots within the blood vessels, thereby using up coagulation factors.

biotransformation

Undergoes desulfation and polymerization via the liver

absorption

Mean absolute bioavailability of enoxaparin, after 1.5 mg/kg given subcutaneously, based on anti-Factor Xa activity is approximately 100% in healthy volunteers.

half life

4.5 hours

route of elimination

Enoxaparin sodium is primarily metabolized in the liver by desulfation and/or depolymerization to lower molecular weight species with much reduced biological potency. Renal clearance of active fragments represents about 10% of the administered dose and total renal excretion of active and non-active fragments 40% of the dose.

drug interactions

Drotrecogin alfa: Combination should be used with caution after weighing advantages and disadvantages. Low molecular weight heparins such as enoxaparin may increase the adverse effects of drotrecogin. Monitor for bleeding if used concomitantly.

Ginkgo biloba: Additive anticoagulant/antiplatelet effects may increase bleed risk. Concomitant therapy should be avoided.

Treprostinil: The prostacyclin analogue, Treprostinil, increases the risk of bleeding when combined with the anticoagulant, Exoxaparin. Monitor for increased bleeding during concomitant thearpy.