Level 2: Mid-level evidence

The American College of Chest Physicians (ACCP) recommends thromboprophylaxis using unfractionated heparin (UFH), low-molecular-weight heparin (LMWH), or fondaparinux (Arixtra) in selected general medical patients. The results of a recent Cochrane review of 13 randomized trials suggest that while LMWH and UFH are similarly effective, LMWH may be safer (Cochrane Database Syst Rev. 2009;[3]:CD003747). In analyses comparing the pooled effects of UFH or LMWH vs. controls (placebo or no treatment), the heparin treatments were associated with reduced rates of deep venous thrombosis (DVT) (2.9% vs. 7.3%, P <.00001) and pulmonary embolism (PE) (0.63% vs. 1.1%, P=.0073), with no significant difference in mortality (5.2% vs. 5.5%). However, the heparin treatments were associated with increased risk of major bleeding (0.49% vs. 0.22%, P =.0042). In a meta-analysis of four trials that directly compared UFH with LMWH, UFH was associated with a significantly higher risk of major bleeding (1.35% vs. 0.34%, P =.015) but no significant differences in DVT, PE, or mortality.