Aspirin may be noninferior to dalteparin for VTE prophylaxis following hip replacements

Aspirin therapy for 28 days may be a reasonable alternative to low-molecular-weight heparin for extended venous thromboembolism (VTE) prophylaxis among hip replacement patients who have already received low-molecular-weight heparin for 10 days, a study found.

Researchers conducted a multicenter, randomized, controlled trial, the EPCAT (Extended Prophylaxis Comparing Low Molecular Weight Heparin to Aspirin in Total Hip Arthroplasty) study, among 778 patients who had elective, unilateral total hip arthroplasty from 2007 to 2010 at 12 tertiary care orthopedic referral centers in Canada.

After an initial 10 days of dalteparin prophylaxis, patients were randomly assigned to 28 days of dalteparin (n=400) or aspirin (n=386). Researchers noted symptomatic VTE confirmed by objective testing (primary efficacy outcome) and bleeding.

Results appeared in the June 4 Annals of Internal Medicine.

The study was halted prematurely because of decreasing enrollment after a major shift in the use of anticoagulant prophylaxis in Canada following the approval of rivaroxaban. This prompted an unplanned interim analysis by the data safety monitoring board, which found that the primary objective of noninferiority of aspirin had been reached.

Of the enrolled patients, five of 398 (1.3%) randomly assigned to dalteparin and one of 380 (0.3%) randomly assigned to aspirin had VTE (absolute difference, 1.0 percentage point; 95% confidence interval [CI], −0.5 to 2.5 percentage points). Aspirin was noninferior (P<0.001) but not superior (P=0.22) to dalteparin. Clinically significant bleeding occurred in five patients (1.3%) receiving dalteparin and two (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 (95% CI, −0.3 to 3.8 percentage points; P=0.091) in favor of aspirin.

The researchers noted that given its low cost and greater convenience, aspirin may be considered a reasonable alternative for extended thromboprophylaxis after total hip arthroplasty.

They wrote, “We believe our findings are valid and generalizable, given that the demographic and surgical characteristics were similar between the groups and the study was performed in several centers involving many orthopedic surgeons. The study design reflected clinical practice in that no screening tests for VTE were performed and the primary events were symptomatic ones that caused patients to seek medical attention.”