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Aspirin As Safe and Effective As LMWH for Extended Thromboprophylaxis after THA


 

Clinical question

Is aspirin as effective as dalteparin for extended venous thromboembolism prophylaxis in patients who have undergone total hip arthroplasty?

Bottom line

Aspirin is as effective as dalteparin for extended thromboprophylaxis in patients who had hip arthroplasty (THA) and had initially received 10 days of dalteparin prophylaxis postoperatively. Because of its relative safety, low cost, and easy administration, aspirin is an attractive alternative to low-molecular-weight heparin (LMWH) when used for this purpose. (LOE = 1b)

Reference

Anderson DR, Dunbar MJ, Bohm ER, et al. Aspirin versus low-molecular-weight heparin for extended venous thromboembolism prophylaxis after total hip arthroplasty. Ann Intern Med 2013;158(11):800-806.

Study design

Randomized controlled trial (double-blinded)

Funding source

Industry

Allocation

Concealed

Setting

Inpatient (any location) with outpatient follow-up

Synopsis

Previous studies have confirmed the benefit of extended thromboprophylaxis with LMWH in patients who have undergone elective THA (EBMG Evidence Summary 3/20/2003). The cost of LMWH and the inconvenience of administering daily subcutaneous injections are high, however. In this study, investigators enrolled patients undergoing elective THA to receive extended thromboprophylaxis with either LMWH, specifically dalteparin, or aspirin. All patients received an initial 8 days to 10 days of postoperative dalteparin prophylaxis. This was followed by randomization to either dalteparin 5000 units daily or aspirin 81 mg daily for the next 28 days. To preserve masking, placebo aspirin tablets and placebo dalteparin injections were also administered. Patients with metastatic cancer or those with conditions that precluded the use of an anticoagulant or aspirin were excluded. An amendment to the initial study protocol allowed patients using long-term aspirin therapy at a dose of less than 100 mg daily to be enrolled. These patients were assigned to either dalteparin or aspirin 81 mg in addition to their usual dose of aspirin. Because of slow recruitment, study enrollment was halted prematurely after 786 patients of a targeted group of 1100 had entered. Baseline characteristics in the 2 groups were similar, with a mean age of 58 years and mean hospital length of stay of 5 days. More than 90% of the patients in the study reported adherence to all doses of the study medications. After a 90-day follow-up period, aspirin was found to be as effective as dalteparin for the prevention of symptomatic venous thromboembolism (1.3% with venous thromboembolism events in the dalteparin group, 0.3% in the aspirin group; P < .001 for noninferiority). There were no differences in clinically significant bleeding events between the 2 groups, although the trend favored aspirin (1.3% with dalteparin vs 0.5% with aspirin). In the subset of patients using long-term aspirin therapy (n = 39), one patient assigned to the aspirin group had a clinically significant, nonmajor bleeding event, but there were no venous thromboembolism events in either group.

Dr. Kulkarni is an assistant professor of hospital medicine at Northwestern University in Chicago.

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