New research findings support the use of aspirin monotherapy after hip or knee arthroplasty, with efficacy and bleeding outcomes comparable to a short course of rivaroxaban followed by aspirin.

The study, presented at the International Society on Thrombosis and Haemostasis (ISTH) conference, found that aspirin alone was non-inferior to a five-day course of rivaroxaban followed by aspirin for preventing post-arthroplasty venous thromboembolism (VTE).

Rates of major or clinically relevant non-major bleeding were similarly low in both treatment groups, supporting aspirin monotherapy as a safe and clinically effective postoperative thromboprophylaxis strategy in these patients.

“As aspirin is a commonly available and inexpensive oral medication, the results of our trial provide strong evidence for clinical decision making when considering an aspirin-alone strategy post-arthroplasty,” said lead author Dr Sudeep Shivakumar, a haematologist at Dalhousie University, Halifax, Canada, when presenting the findings at the ISTH conference in Paris, France.

In the study, now also published in the New England Journal of Medicine [link here], patients in Canada (mean age 67 years, 57% female) who had undergone total hip or knee arthroplasty were randomised to receive 81mg of aspirin (n=2,718) or 10mg of oral rivaroxaban (n=2,647) for the first five days after surgery.

All patients then received 81mg of aspirin daily for nine more days after knee arthroplasty or for 30 more days after hip arthroplasty.

In the 90 days following surgery, 12 patients (0.45%) given rivaroxaban and aspirin developed proximal deep vein thrombosis or pulmonary embolism, compared to 13 (0.48%) who received aspirin alone (p<0.001 for non-inferiority).

Similar findings were observed when distal deep vein thrombosis was added to the composite VTE endpoint, with 28 events (1.03%) and 23 events (0.87%) in the aspirin and rivaroxaban groups, respectively.

Over the same time frame, the rate of major bleeding events was similar for both the aspirin alone and rivaroxaban plus aspirin groups (0.44% vs 0.30%), as were rates of clinically relevant non-major bleeding (1.21% vs 1.74%).

Similarly, the rate of either major or clinically relevant non-major bleeding was comparable for both the aspirin alone and rivaroxaban plus aspirin groups (1.66% vs 2.04%).

Three patients died in each cohort, with one death in the rivaroxaban plus aspirin group attributed to pulmonary embolism.

The researchers noted that the overall rate of VTE was lower in their trial than in previous studies, and that the vast majority of patients were classified as standard risk on the STOP-VTE risk-assessment model, with only 3.4% classified as high risk.

“As such, an individualised strategy should be considered if a patient is identified as being at higher risk for VTE,” they wrote.

Responding to an audience member’s question after his presentation, Dr Shivakumar said the next step would be evaluate aspirin monotherapy in patients at higher risk of VTE and compare it with other anticoagulants, particularly apixaban.