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The risk for venous thromboembolism (VTE) persists for several weeks after a major orthopedic procedure, leading to recommendations that anticoagulant therapy continue for up to 5 weeks postoperatively. Such prophylaxis can be accomplished by daily subcutaneous injections of low-molecular-weight heparin (LMWH), but this adds to the discomfort and cost of the procedure.
To determine if aspirin might be a safe and effective substitute for LMWH in this setting, Canadian investigators conducted a multicenter, blinded, randomized, controlled trial involving 778 participants who underwent total hip arthroplasty. All patients initially received dalteparin LMWH (5000 U daily by subcutaneous injection) for 8 to 10 days postoperatively and then were randomized to continue dalteparin or receive aspirin (81 mg daily) for 28 more days.
During a 90 day follow-up period, VTE events occurred in 5 dalteparin recipients (1.3%) and in 1 aspirin recipient (0.3%), indicating that aspirin was noninferior (P<0.001) but not superior (P=0.22) to dalteparin. Major bleeding occurred in 1 dalteparin recipient and no aspirin recipients; clinically significant nonmajor bleeding events occurred in 4 dalteparin recipients and 2 aspirin recipients. A composite analysis of VTE and bleeding events favored aspirin (0.8% vs. 2.5%, P=0.09).
Anderson DR et al. Aspirin versus low-molecular-weight heparin for extended venous thromboembolism prophylaxis after total hip arthroplasty: A randomized trial. Ann Intern Med 2013 Jun 4; 158:800. (http://dx.doi.org/10.7326/0003-4819-158-11-201306040-00004)
Comment
This investigation suggests that aspirin is as safe and effective as dalteparin LMWH. However, only 17.7% of screened patients participated in the trial, and very few events occurred, so the results might not be generalizable to the larger population of patients undergoing hip arthroplasty or other major orthopedic procedures. Nevertheless, future studies assessing new antithrombotic agents should include aspirin as a comparator.