OBJECTIVES: Patients undergoing elective THR surgery are at an increased risk for VTEs.  Even though dalteparin and enoxaparin have proven clinical effectiveness in placebo controlled studies, there have been no head-to-head trials to assess comparative effectiveness.  Meta-analytic techniques were used for an indirect statistical comparison on the safety and efficacy between dalteparin and enoxaparin in patients undergoing THR surgery. METHODS: A literature search of major databases was conducted from 1980 to 2009 for randomized placebo controlled trials evaluating both agents in THR patients.  Binary outcomes (e.g. VTE rates) for the LMWH group relative to control group were statistically pooled using fixed or random effects models in cases of significant heterogeneity.  In trials where a common control was used, indirect statistical comparisons between dalteparin and enoxaparin were performed using meta regression analysis with active drug (dalteparin or enoxaparin) as the primary independent variable. RESULTS: A total of nine placebo controlled enoxaparin (n=5) and dalteparin (n=4) trials met the inclusion criteria.  The meta analysis of all trial data showed that THR patients treated with enoxaparin or dalteparin had a 54% VTE relative risk reduction compared to the placebo (RR = 0.46, p <0.001).  This benefit was achieved without a significant increase in the risk for major bleeds (RR = 1.14, p = 0.80), heparin induced thrombocytopenia (HIT) (RR = 0.83, p = 0.75) or death (RR = 0.77, p = 0.61).  The indirect statistical comparison was not able to find significant differences between enoxaparin and dalteparin in terms of VTEs (p=0.86), risk of major bleeds (p=0.46), HIT (p=0.75) and death (p=1.0). CONCLUSIONS: The findings of the analysis suggest comparable safety and efficacy between dalteparin and enoxaparin in THR patients. Therefore, treatment decisions should be based on other considerations such as patient or physician preference, ease of administration and cost.