Pharmacological venous thromboembolism prophylaxis in hospitalized medical patients - A meta-analysis of randomized controlled trials

Background: There is uncertainty regarding which pharmacological agents most effectively prevent venous thromboembolism in hospitalized medical patients. We therefore performed a meta-analysis to determine this. Methods: MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched from 1950, 1966, and 1800, respectively, through June 30, 2006, for randomized controlled trials that involved medical patients comparing unfractionated heparin (UFH) or low-molecular-weight heparin or heparinoid (LMWH) with a control, LMWH with UFH, or selective factor Xa inhibitors with a comparator. Study selection, validity assessment, and data abstraction were performed by 2 independent reviewers (L. W. and S. W.). Data synthesis was undertaken by 1 blinded investigator (S.J.H.). Results: Thirty-six studies were included. Compared with the control, UFH was associated with a reduced risk of deep venous thrombosis (DVT) (risk ratio [RR], 0.33; 95% confidence interval [CI], 0.26-0.42) and pulmonary embolism (RR, 0.64; 95% CI, 0.50-0.82), as was LMWH (RR, 0.56; 95% CI, 0.45-0.70; and RR, 0.37; 95% CI, 0.21-0.64, respectively). A UFH dosage of 5000 U 3 times daily was more effective in preventing DVT than a UFH dosage of 5000 U twice daily when compared with the control (RR, 0.27; 95% CI, 0.20-0.36; vs RR, 0.52; 95% CI, 0.28-0.96). Neither UFH nor LMWH reduced mortality. When directly compared with UFH, LMWH was associated with a lower risk of DVT (RR, 0.68; 95% CI, 0.52-0.88) and injection site hematoma (RR, 0.47; 95% CI, 0.36-0.62), but no difference was seen between the 2 agents in the risk of bleeding or thrombocytopenia. Conclusions: Both UFH and LMWH reduce venous thromboembolic risk in hospitalized medical patients, but neither agent alters mortality. When directly compared, LMWH is more effective in preventing DVT.