Potential indications
The three leading factor XI inhibitors have slightly different phase 3 development programs.
Dr. Ruff notes that not every agent is being investigated in phase 3 trials for all the potential indications, but all three are going for the AFib indication. “This is by far the biggest population, the biggest market, and the biggest clinical need for these agents,” he says.
While the milvexian and asundexian trials are using an active comparator – pitting the factor XI inhibitors against apixaban in AFib patients – the Anthos LILAC trial is taking a slightly different approach and is comparing abelacimab with placebo in patients with AFib who are not currently taking an anticoagulant because of concerns about bleeding risk.
Janssen/BMS is conducting two other phase 3 trials of milvexian in their LIBREXIA phase 3 program. Those trials involve poststroke patients and ACS patients. Bayer is also involved in a poststroke trial of asundexian as part of its OCEANIC phase 3 program.
Dr. Ruff points out that anticoagulants currently do not have a large role in the poststroke or post-ACS population. “But the hope is that, if factor XI inhibitors are so safe, then there will be more enthusiasm about using an anticoagulant on top of antiplatelet therapy, which is the cornerstone of therapy in atherosclerotic cardiovascular disease.”
In addition to its phase 3 LILAC study in patients with AFib, Anthos is conducting two major phase 3 trials with abelacimab for the treatment of cancer-associated venous thromboembolism.
Dr. Ruff notes that the indication of postsurgery or general prevention of VTE is not being pursued at present.
“The orthopedic surgery studies were done mainly for dose finding and proof of principle reasons,” he explains. “In orthopedic surgery the window for anticoagulation is quite short – a few weeks or months. And for the prevention of recurrent VTE in general in the community, those people are at a relatively low risk of bleeding, so there may not be much advantage of the factor XI inhibitors, whereas AFib patients and those with stroke or ACS are usually older and have a much higher bleeding risk. I think this is where the advantages of an anticoagulant with a lower bleeding risk are most needed.”
Dr. Alexander points out that to date anticoagulants have shown more efficacy in venous clotting, which appears to be more dependent on coagulation factors and less dependent on platelets. “Atrial fibrillation is a mix between venous and arterial clotting, but it has more similarities to venous, so I think AFib is a place where new anticoagulants such as the factor XI inhibitors are more likely to have success,” he suggests.
“So far, anticoagulants have had a less clear long-term role in the poststroke and post-ACS populations, so these indications may be a more difficult goal,” he added.
The phase 3 studies are just starting and will take a few years before results are known.
Differences between the agents
The three factor XI inhibitors also have some differences. Dr. Ruff points out that most important will be the safety and efficacy of the drugs in phase 3 trials.
“Early data suggest that the various agents being developed may not have equal inhibition of factor XI. The monoclonal antibody abelacimab may produce a higher degree of inhibition than the small molecules. But we don’t know if that matters or not – whether we need to achieve a certain threshold to prevent stroke. The efficacy and safety data from the phase 3 trials are what will primarily guide use.”
There are also differences in formulations and dosage. Abelacimab is administered by subcutaneous injection once a month and has a long duration of activity, whereas the small molecules are taken orally and their duration of action is much shorter.
Dr. Ruff notes: “If these drugs cause bleeding, having a long-acting drug like abelacimab could be a disadvantage because we wouldn’t be able to stop it. But if they are very safe with regard to bleeding, then having the drug hang around for a long time is not necessarily a disadvantage, and it may improve compliance. These older patients often miss doses, and with a shorter-acting drug, that will mean they will be unprotected from stroke risk for a period of time, so there is a trade-off here.”
Dr. Ruff says that the AZALEA phase 2 study will provide some data on patients being managed around procedures. “The hope is that these drugs are so safe that they will not have to be stopped for procedures. And then the compliance issue of a once-a-month dosing would be an advantage.”
Dr. Patel says he believes there is a place for different formations. “Some patients may prefer a once-monthly injection; others will prefer a daily tablet. It may come down to patient preference, but a lot will depend on the study results with the different agents,” he commented.
What effect could these drugs have?
If these drugs do show efficacy in these phase 3 trials, what difference will they make to clinical practice? The potential appears to be very large.
“If these drugs are as effective at preventing strokes as DOACs, they will be a huge breakthrough, and there is good reason to think they would replace the DOACs,” Dr. Alexander says. “It would be a really big deal to have an anticoagulant that causes almost no bleeding and could prevent clots as well as the DOACs. This would enable a lot more patients to receive protection against stroke.”
Dr. Alexander believes the surgery studies are hopeful. “They show that the factor XI inhibitors are doing something to prevent blood clots. The big question is whether they are as effective as what we already have for the prevention of stroke and if not, what is the trade-off with bleeding?”
He points out that, even if the factor XI inhibitors are not as effective as DOACs but are found to be much safer, they might still have a potential clinical role, especially for those patients who currently do not take an anticoagulant because of concerns regarding bleeding.
But Dr. Patel points out that there is always the issue of costs with new drugs. “New drugs are always expensive. The DOACS are just about to become generic, and there will inevitably be concerns about access to an expensive new therapy.”
Dr. Alexander adds: “Yes, costs could be an issue, but a safer drug will definitely help to get more patients treated and in preventing more strokes, which would be a great thing.”
Dr. Patel has received grants from and acts as an adviser to Bayer (asundexian) and Janssen (milvexian). Dr. Alexander receives research funding from Bayer. Dr. Ruff receives research funding from Anthos for abelacimab trials, is on an AFib executive committee for BMS/Janssen, and has been on an advisory board for Bayer.
A version of this article first appeared on Medscape.com.