Aspirin has been shown to be as effective as the direct acting oral anticoagulant (DOAC) rivaroxaban as extended prophylaxis against venous thromboembolism (VTE) following hip or knee arthroplasty.
In a randomised controlled trial involving 3424 patients who received an initial five days of rivaroxaban prophylaxis, there was no difference in VTE incidence among those randomised to use aspirin 81mg daily for a further nine days (knee arthroplasty) or 30 days (hip arthroplasty) compared to those who continued on the DOAC.
After 90 days of follow up, VTE occurred in 11 of 1707 aspirin patients (0.64%) and in 12 of 1717 rivaroxaban extended prophylaxis patients (0.70%), the Canadian trial showed.
Clinically important bleeding events occurred in 1.29% of aspirin patients and 0.99% of rivaroxaban patients.
The study authors, led by Dr David Anderson, a haematologist at Dalhouse University, Nova Scotia, said aspirin was a potentially good choice for extended prophylaxis after arthroplasty because it was inexpensive and widely available. However until now there had been no trials comparing it with direct acting oral anticoagulants.
“Our findings are clinically important,” they wrote in NEJM. “The trial was large and adequately powered to show the noninferiority of aspirin as compared with rivaroxaban.”
They added that no differences were seen in subgroups of patients in the trial, although there was a suggestion of more major and clinically relevant nonmajor bleeding among patients who were already taking long-term aspirin and who were receiving a second daily dose of aspirin prophylaxis.
“The EPCAT II trial provides additional information to support the use of aspirin for the secondary prevention of VTE after joint arthroplasty,” they concluded.
The findings appear to support current recommendations for VTE prophylaxis from the Arthroplasty Society of Australia.
Their guidelines note that many several large studies have not demonstrated improved VTE prophylaxis or improved all-cause mortality with more aggressive chemoprophylaxis medications compared to aspirin.
The Society’s guidelines state that aspirin 100-300mg per day is an option for patients with routine risk of VTE, and rivaroxaban is suggested as an option for patients with a high risk of VTE.
However a draft Clinical Care Standard on VTE prophylaxis released by the Australian Commission on Safety and Quality in Health Care in 2017 said the use of aspirin as a single agent for the primary prevention of VTE in hip and knee replacement surgery was controversial.
In the absence of a national Australian clinical practice guideline for the primary prevention of VTE, the Commission conducted a review of evidence, whose findings were deemed are “equivocal”.
The ACSQHC standard noted the Canadian trial was underway and “It is likely that their findings, when published, will greatly assist in clarifying the safety and efficacy of staged protocols [of aspirin for VTE prophylaxis following arthroplasty].