Anticoagulation

Heparins

Unfractionated Heparin - This is used for therapeutic anticoagulation peri-operatively, or if there's a significant bleeding risk. It works by activating Antithrombin. The benefit of this is that it works very quickly and has a very short-half life, allowing it to provide interim anticoagulation. This requires monitoring as it consists of a variety of chain lengths, so its effects are less predictable.

LMWH (e.g. Dalteparin, Enoxaparin) - This is used for VTE prophylaxis and treatment. It works by inactivating Factor Xa. This doesn't require monitoring as it only consists of short-chain heparins, so its effects are more predictable. Side-effects of these include bleeding and Heparin-induced Thrombocytopenia (HIT). To reverse its effects, Protamine Sulphate can be given.

Both of these agents can effectively be given in any pre-operative or admitted patient as VTE prophylaxis, but LMWHs are generally preferred as it can be given once daily (longer half-life) and has a lower risk of heparin-induced thrombocytopenia. The only disadvantage is that LMWH costs more than low-dose UFH.

Warfarin

This is used for long-term anticoagulation. It works by reducing production of Vit K-dependant clotting factors (Factors 2, 7, 9, 10). Its effects are regularly monitored with the INR.

N.B. A good way of remembering these factors is "1972".

It's contraindications include Bleeding disorders, Peptic ulcer, and Pregnancy (teratogen).

N.B. Important to note that warfarin is initially prothrombotic. So, when initiating, patients are usually bridged with a LMWH for 5 days whilst the INR adjusts to the intended range (commonly 2-3).

DOACs

Examples of these are:

• Rivaroxaban, Apixaban - Factor Xa inhibitors

• Dabigatran - Direct Thrombin inhibitor

These don't require monitoring.