Mechanism of Action
Enoxaparinum is classified as an antithrombin III-dependent anticoagulant. This means the drug has no intrinsic anticoagulant activity on its own; to exert its effect, it must bind to endogenous antithrombin III.
Like all low-molecular-weight heparins, enoxaparin inhibits factor Xa and thrombin (factor IIa). However, the degree of this inhibition varies. The key pharmacodynamic feature of enoxaparin is its high ratio of anti-Xa activity to anti-thrombin activity, which is 3.8:1. For comparison, this ratio is lower in other members of the group: 3.2–3.5:1 for nadroparin and reviparin, and 2.2–2.7:1 for dalteparin.
Place in the Anticoagulant Classification
Enoxaparin belongs to the broad group of antithrombin III-dependent agents. To understand its place in therapy, it is important to review the full classification:
- Standard (Unfractionated) Heparin: Heparin sodium and heparin calcium.
- Low-Molecular-Weight Heparins (LMWHs): Enoxaparin sodium, nadroparin calcium, dalteparin sodium, reviparin sodium.
- Factor Xa Inhibitors: Fondaparinux sodium.
- Heparinoids: Sulodexide, danaparoid sodium. These are sulfated glycosaminoglycans derived from porcine intestinal mucosa. Structurally related to heparins with a similar mechanism of action, they are classified separately due to differences in physicochemical characteristics.
Pharmacological Features of the LMWH Group
It is essential to note that LMWH preparations (such as enoxaparin, nadroparin, dalteparin) are heterogeneous. They represent different fractions, meaning they are not identical and cannot be substituted for one another in equivalent doses.
Differences among these agents involve:
- Composition and physicochemical properties.
- Molecular weight (MW). For example, the MW of dalteparin sodium is 5,000–6,000 Da, whereas other agents (reviparin, nadroparin) range from 3,900 to 4,500 Da.
- Biological activity (varying anti-Xa to anti-IIa ratios).
Despite this structural heterogeneity, the pharmacokinetics within the group differ only slightly.
Drug Interactions
When prescribing anticoagulant therapy, the impact of concomitant medications must be considered, particularly in patients with endocrine disorders.
Heparins can cause a decrease in the hypoglycemic effect of insulin therapy. This counter-regulatory action creates a risk of hyperglycemia.
For differential recall: A decrease in insulin efficacy is also caused by thiazide diuretics, glucocorticoids, and thyroid hormones. Conversely, an enhancement of the hypoglycemic effect (risk of hypoglycemia) is provoked by $\beta$-blockers (which additionally mask symptoms of hypoglycemia), sulfonamides, anabolic steroids, and MAO inhibitors.
Formulation and Prescribing Guidelines
Enoxaparin sodium is widely known under the brand name Clexane.
Formulation: Solution in pre-filled syringes containing 10,000 anti-Xa IU/mL. Available syringe volumes: 0.2, 0.4, and 0.8 mL.
Dose Calculation:
- 1 mL of solution contains 0.1 g (100 mg) of enoxaparin.
- 0.001 g (1 mg) of enoxaparin equals 100 anti-Xa IU.
Administration: The drug is administered strictly subcutaneously (SC). The standard prophylactic dosage is 20–40 mg once daily. In terms of activity, this is equivalent to 2,000–4,000 anti-Xa IU, corresponding to a volume of 0.2–0.4 mL of the standard syringe solution.