💊 Low Molecular Weight Heparin

Low Molecular Weight Heparins (LMWHs) are a class of anticoagulant medications derived from unfractionated heparin. They have a more predictable anticoagulant response than unfractionated heparin.

LMWHs exert their anticoagulant effect primarily by potentiating the action of antithrombin III, leading to the inactivation of Factor Xa. They have less effect on thrombin (Factor IIa) compared to unfractionated heparin.

LMWHs are widely used for the prophylaxis of venous thromboembolism (VTE) in surgical and medical patients, as well as during pregnancy. They are also indicated for the treatment of established deep vein thrombosis (DVT) and pulmonary embolism (PE), often as bridging therapy or for long-term management. LMWHs are used in unstable angina and non-ST-elevation myocardial infarction (NSTEMI).

Absolute contraindications include active major bleeding, a history of heparin-induced thrombocytopenia (HIT), and severe uncontrolled hypertension. LMWHs are also contraindicated in patients with severe renal impairment (depending on the specific LMWH) and in those with acute bacterial endocarditis. Caution is advised in patients with a high risk of bleeding, such as recent surgery or peptic ulcer disease.

The most common adverse effect is bleeding, which can range from minor bruising at the injection site to major haemorrhage. Heparin-induced thrombocytopenia (HIT) is a rare but serious immune-mediated complication. Other side effects include injection site reactions, osteoporosis with long-term use, and hypersensitivity reactions. Hyperkalaemia can also occur due to aldosterone suppression.

Routine coagulation monitoring (e.g., APTT) is generally not required due to the predictable dose-response relationship. However, in certain situations such as severe renal impairment, obesity, or pregnancy, anti-Xa levels may be monitored. Platelet counts should be monitored regularly, especially during the initial phase of treatment, to detect HIT.

Always check for active bleeding, a history of HIT, and severe renal impairment. Ensure the correct dose is prescribed based on indication and patient weight (if applicable). Counsel patients on subcutaneous injection technique, the importance of adherence, and to report any unusual bruising or bleeding. Be aware of potential interactions with other antiplatelet or anticoagulant agents.

LMWHs are preferred over UFH for many indications due to their longer half-life, subcutaneous administration, and lower incidence of HIT. Enoxaparin and dalteparin are common examples. Remember that LMWHs are renally excreted, so dose adjustment or alternative anticoagulation may be needed in renal failure. Protamine sulfate can partially reverse the effects of LMWH.

SBAs often test the appropriate use of LMWH for VTE prophylaxis in different clinical scenarios (e.g., post-surgery, medical inpatients). Questions may also focus on the management of established DVT/PE, including bridging to oral anticoagulation. Recognising the signs and management of HIT is a high-yield topic.