By: 31 December 2018
Aspirin alone is a good clot buster after knee surgery

When it comes to preventing blood clots after a knee replacement, aspirin may be just as effective as newer, more expensive drugs.

After knee surgery, there’s a risk of blood clots in the legs or lungs,so it’s routine for patients to take clot-preventing drugs for some time afterward.

Some doctors choose powerful anti-clotting drugs like heparin (Lovenox)and rivaroxaban (Xarelto), but it hasn’t been clear whether these expensive prescription drugs work any better than cheap, readily available aspirin.

“Aspirin alone may provide similar protection compared to anticoagulation treatments,” said Brian Hallstrom, orthopaedic surgeon and associate chair for quality and safety at the University of Michigan (UM)Department of Orthopaedic Surgery.

Hallstrom is the lead author of a new study published in JAMASurgery that found few patients developed a blood clot after surgery, and those patients on aspirin fared just as well as those on anticoagulants.

During the two-year study period from 2013 to 2015, aspirin use rose from 10 per cent to 50 per cent among the patients cared for by orthopaedic surgeons in the Michigan Arthroplasty Registry Collaborative QualityInitiative, a statewide effort to give patients the best possible recovery and outcomes after hip and knee replacements.

Since then, the shift has become even more distinct: Aspirin prescribing has risen to 70 per cent among Michigan surgeons, says Hallstrom, who is co-director of the initiative and a health services researcher at UM’sInstitute for Healthcare Policy and Innovation.

Based on the experience of 41,537 Michigan patients undergoing knee replacement, the study may further the debate about the routine use of aspirin for clot prevention.

The new UM study suggests patients may be adequately protected if they take aspirin alone from day one.

“This study is truly a real-world experience of what happened inMichigan when the majority of surgeons switched to aspirin,” Hallstrom said.“The incidence of blood clots, pulmonary embolus and death did not increase despite this dramatic change in practice.”

These days, most patients have a generally low risk of blood clots after knee replacement for a number of reasons. Those reasons include shorter surgical times, less invasive procedures and use of regional anaesthesia that allows early mobilisation after surgery, Hallstrom said. Some patients are even going home the same day.

“The most important way to prevent blood clots is getting moving,” said Hallstrom, noting that people are at risk for blood clots when they sit or lie in one position for too long, such as on an airplane or a hospital bed.

The UM study involved patients undergoing knee replacement surgery at any of the 29 Michigan hospitals in the surgical quality group. One-third of the patients took aspirin alone; 54 per cent took only an anticoagulant; and 13per cent took an aspirin/anticoagulant combination.

Over three months, just 1.16 per cent of aspirin patients developed a serious blood clot. That was true for 1.42 per cent of anticoagulant patients,according to the Michigan study. This was not statistically different.

So, neither drug appeared better than the other, but aspirin has some obvious advantages.

“Aspirin is easy to take and much less expensive,” Hallstrom said.“Patients can get it over the counter for pennies, while the other anticoagulants require monitoring, injections, frequent dose adjustments and are extremely expensive.”

The reported cost for a 30-day supply of rivaroxaban is approximately $379 to $450; heparin is estimated at $450 to $890. Although warfarin costs a few dollars for a 30-day supply, its cost approaches that of the other anticoagulants when doctor visits for monitoring are factored in, Hallstrom says. In contrast, aspirin costs approximately $2 a month.

The study suggests most patients can have just aspirin without increasing the risk for venous thromboembolism, but doctors need to consider factors such as a patient’s history of clots, obesity and ability to mobilise after surgery when determining the best measure for clot prevention, Hallstrom added.

Source: Michigan Medicine