Intervention: After an initial 10 days of dalteparin prophylaxis after elective THA, patients were randomly assigned to 28 days of dalteparin (n = 400) or aspirin (n = 386).
Measurements: Symptomatic VTE confirmed by objective testing (primary efficacy outcome) and bleeding.
Results: Five of 398 patients (1.3%) randomly assigned to dalteparin and 1 of 380 (0.3%) randomly assigned to aspirin had VTE (absolute difference, 1.0 percentage point [95% CI, −0.5 to 2.5 percentage points]). Aspirin was noninferior (P less than 0.001) but not superior (P = 0.22) to dalteparin. Clinically significant bleeding occurred in 5 patients (1.3%) receiving dalteparin and 2 (0.5%) receiving aspirin. The absolute between-group difference in a composite of all VTE and clinically significant bleeding events was 1.7 percentage points (CI, −0.3 to 3.8 percentage points; P = 0.091) in favor of aspirin.
Limitation: The study was halted prematurely because of difficulty with patient recruitment.
Conclusion: Extended prophylaxis for 28 days with aspirin was noninferior to and as safe as dalteparin for the prevention of VTE after THA in patients who initially received dalteparin for 10 days. Given its low cost and greater convenience, aspirin may be considered a reasonable alternative for extended thromboprophylaxis after THA.
I wonder whether either treatment did anything. Evidence favoring the extended phase (beyond 10 days) of prophylaxis must be somewhat weak, as the ACCP guidelines do not give it a definite recommendation (they only suggest it).