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Warfarin best for thrombotic antiphospholipid syndrome?



Patients with thrombotic antiphospholipid syndrome are better treated with a vitamin K antagonist, such as warfarin, rather than a direct oral anticoagulant (DOAC), a new systematic review and meta-analysis suggests.

“Our study is showing that in randomized controlled trials in patients with thrombotic antiphospholipid syndrome, the risk of arterial thrombotic events, particularly stroke, is significantly increased with DOACs vs. vitamin K antagonists,” senior author, Behnood Bikdeli, MD, Brigham and Women’s Hospital, Boston, told this news organization. “These results probably suggest that DOACs are not the optimal regimen for patients with thrombotic antiphospholipid syndrome.”

The study was published online in the Journal of the American College of Cardiology.

Autoimmune disorder

Thrombotic antiphospholipid syndrome is a systemic autoimmune disorder characterized by recurrent arterial and/or venous thrombotic events.

Dr. Bikdeli estimates that antiphospholipid syndrome is the cause of 50,000-100,000 strokes, 100,000 cases of myocardial infarction, and 30,000 cases of deep vein thrombosis every year.

“It is a serious condition, and these are a high-risk and complex group of patients,” he said.

The standard treatment has been anticoagulation with a vitamin K antagonist such as warfarin. “But this is a cumbersome treatment, with many drug interactions and the need for INR [International Normalized Ratio] monitoring, which can be difficult to manage in patients with antiphospholipid syndrome as there can sometimes be falsely abnormal numbers,” Dr. Bikdeli noted. “Because of these challenges, it looked very promising to explore the use of DOACs in this population.”

Four main randomized trials have been conducted to investigate the use of DOACs in antiphospholipid syndrome – three with rivaroxaban and one with apixaban. “These trials were all quite small and, while they did not show definite results, some of them suggested nonsignificant findings of slightly worse outcomes for DOACs vs. vitamin K antagonists. But there is a lot of uncertainty, and it is difficult to look at subgroups in such small trials,” Dr. Bikdeli said. “There are many questions remaining about whether we should use DOACs in patients with antiphospholipid syndrome and, if so, which particular subgroups.”

The authors therefore performed a systematic review and meta-analysis of randomized controlled trials that compared DOACs with vitamin K antagonists in patients with antiphospholipid syndrome. They also contacted the principal investigators of the trials to obtain additional unpublished aggregate level data on specific subgroups.

Four open-label randomized controlled trials involving 472 patients were included in the meta-analysis.

Overall, the use of DOACs, compared with vitamin K antagonists, was associated with increased odds of subsequent arterial thrombotic events (odds ratio, 5.43; P < .001), especially stroke.

The odds of subsequent venous thrombotic events or major bleeding were not significantly different between the two groups. Most findings were consistent within subgroups.

“Our results show that use of DOACs vs. vitamin K antagonists is associated with increased risk of arterial thrombotic events – a risk that is primarily driven by a significant increase in the risk of stroke,” Dr. Bikdeli commented.

When looking at subgroups of interest, it was previously thought that DOACs may not be so effective in the so-called “triple-positive” antiphospholipid patients. These patients have three different types of antibodies and have the highest risk of thrombosis, Dr. Bikdeli noted.

“But one of the interesting findings of our study is that the results are actually consistent in women vs. men and in people who have triple-positive antibodies and those who had double- or single-positive antibodies,” he said. “Our analyses did not show effect modification by antibody subgroups. They suggest similar trends towards worse outcomes in all subgroups.”

“From these results, I would be similarly concerned to use DOACs even if someone has double-positive or single-positive antiphospholipid antibodies,” he added.

Dr. Bikdeli said he would still recommend shared decision-making with patients. “If I have a patient who has thrombotic antiphospholipid syndrome, I would share my reservation about DOACs, but there are multiple factors that come into decision-making. If someone has difficulty with checking INRs, we may make an informed choice and still use a DOAC, but patients need to know that there is likely an excess risk of subsequent arterial events with DOACs, compared with a vitamin K antagonist.”

He noted that it is still not completely clear on the situation for people with single-positive antiphospholipid syndrome or the type of antibody that is present. It is also possible that a higher dose of DOAC could be more effective, a strategy that is being investigated in a separate randomized trial currently ongoing.

“But for routine practice I would have concerns about using DOACs in antiphospholipid syndrome patients in general,” he said. “For triple positive there is more data and greater concern, but I wouldn’t give a pass for a double- or single-positive patient either.”

The reason why DOACs would be less effective than vitamin K antagonists in antiphospholipid syndrome is not known.

“That is the million-dollar question,” Dr. Bikdeli commented. “DOACs have been such helpful drugs for many patients and clinicians as well. But we have seen that they are not optimal in a series of scenarios now – patients with mechanical heart valves, patients with rheumatic [atrial fibrillaton], and now patients with thrombotic antiphospholipid syndrome.”

One hypothesis is that these patients have some more components of inflammation and are more prone to blood clots, and because vitamin K antagonists work at several parts of the coagulation cascade, they might be more successful, compared with the more targeted DOAC therapy. “But I think we need more studies to fully understand this,” he said.


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