Low-molecular weight heparin

Low-molecular-weight heparin (LMWH) is a class of anticoagulant medications used in the prevention and treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE). LMWHs are derived from unfractionated heparin by chemical or enzymatic depolymerization, resulting in shorter chains of polysaccharides. Compared to unfractionated heparin, LMWHs have more predictable pharmacokinetic properties, require less monitoring, and have a lower risk of osteoporosis and heparin-induced thrombocytopenia (HIT).

Mechanism of Action

LMWHs exert their anticoagulant effect primarily by binding to antithrombin III (ATIII) and potentiating its inhibition of factor Xa. Unlike unfractionated heparin, LMWHs have a higher ratio of anti-factor Xa to anti-factor IIa activity. This selective inhibition of factor Xa with less effect on thrombin (factor IIa) is thought to contribute to their improved safety and efficacy profile.

Indications

LMWHs are indicated for the prevention and treatment of DVT and PE. They are also used in the management of acute coronary syndromes (ACS), including unstable angina and non-ST elevation myocardial infarction (NSTEMI). In certain cases, LMWHs are used in the prophylaxis of ischemic complications in patients undergoing percutaneous coronary intervention (PCI) or during the acute management of ST-elevation myocardial infarction (STEMI) in conjunction with other antithrombotic agents.

Administration

LMWHs are administered subcutaneously. The dose and duration of treatment depend on the indication, patient's body weight, and renal function. Monitoring of anti-factor Xa levels may be necessary in patients with renal impairment, pregnant women, or individuals at extremes of body weight.

Adverse Effects

The most common adverse effect of LMWHs is bleeding. Other potential side effects include HIT, although the risk is significantly lower than with unfractionated heparin. Long-term use of LMWHs can also lead to osteoporosis.

Examples

Some examples of LMWHs include enoxaparin, dalteparin, and tinzaparin. Each of these medications has specific indications, dosing regimens, and monitoring requirements.

Comparison with Other Anticoagulants

LMWHs offer several advantages over unfractionated heparin, including a lower risk of HIT, less frequent dosing, and the possibility of outpatient treatment for certain conditions. Compared to newer oral anticoagulants (NOACs), LMWHs require subcutaneous administration, which may be a disadvantage for some patients. However, LMWHs have a longer track record and specific antidotes are not required for reversal of their anticoagulant effect.