Low-Dose Unfractìonated Heparin (LDUH) – LDUH binds with antithrom-bin III to inhibit factor Ha (thrombin) and factor Xa (intrinsic clotting pathway).

Low-Molecular-Weight Heparin (LMWH) – Mechanism of action is similar to LDUH, but the reduced binding with plasma proteins results in a longer and more predictable half-life. It is contraindicated in heparin-induced thrombocytopenia (HIT).¹ Enoxapańn (Lovenox), 30 mg SC bid or 40 mg qd, is FDA-approved for s/p THA; 30 mg bid is approved for s/p TKA. Daltepańn (Fragmin), 5,000 U SC qd, is FDA-approved for s/p THA.

Vitamin K antagonist (VKA or Warfarin¹) – It inhibits the vitamin K-mediated production of procoagulant factors X, IX, VII, and II (extrinsic pathway) and anticoagulant proteins C and S. There is an initial paradoxical pro-coagulant effect since proteins C and S are depleted first (thus, initiating therapy with “loading” doses >5 mg qd is not usually recommended).

For INRs 5 to 9 w/o significant bleeding, give 1 to 2.5 mg po vitamin K or follow INRs w/o vitamin K. For INRs > 9 w/o significant bleeding, give 3 to 5 mg po vitamin K and monitor INRs (repeat vitamin K if necessary). For elevated INRs with serious bleeding, give 10 mg vitamin K by slow IV infusion (repeat ql2h if necessary) and supplement with plasma or prothrombin complex concentrate.

Fondaparinux, 2-5 mg SC qd (Arixtra) – This is a heparin derivative that selectively inhibits factor Xa and is FDA-approved for s/p hip fracture surgery (HFS), THA, and TKA.

Others – Hirudins (e.g., lepirudin, 15 mg SC bid) are direct thrombin inhibitors indicated in the setting of HIT. Heparìnoids (e.g., danaparoid, no longer available for nonmedical reasons) have a similar mechanism of action as that of UH, but do not contain heparin and are also used in the setting of HIT. ASA inhibits platelet aggregation, but is not recommended by the American College of Chest Physicians (ACCP) for DVT prophylaxis because other measures are more efficacious.¹ Infeńor vena cava filters are used for pulmonary embolism (not DVT) prophylaxis.