Despite the recent advent of novel oral anticoagulants, the much-maligned warfarin remains the only current option available for patients who have received a mechanical valve. Now the first trial to explore this indication for a newer oral anticoagulant has suffered a setback.
Last year Boehringer Ingelheim announced the launch of the RE-ALIGN trial, a phase 2, open-label, 12-week randomized comparison of warfarin and dabigatran (Pradaxa) in 400 patients who received a mechanical valve. There were two arms in the trial. The first arm randomized patients during their initial hospital stay. The second arm randomized patients more than 3 months after their surgery.
Now, following the advice of the trial’s Data Safety Monitoring Board, Boehringer Ingelheim said it had discontinued the first arm of the trial, the post-surgery arm, due to “lower than projected plasma levels of dabigatran in this population, and an imbalance in reports of thromboembolic events (primarily strokes).” The trial’s second arm with patients who received a valve more than 3 months before enrollment in the trial is unaffected by this decision and will continue as planned.
Boehringer-Ingelheim said that the news about RE-ALIGN does “not affect the positive benefit/risk profile of Pradaxa 150 mg for the current labeled indication” of stroke prevention in patients with non-valvular atrial fibrillation. “RE-ALIGN is evaluating a different patient population and different doses than were studied in the RE-LY trial.”
Dabigatran has been approved in Europe, but not in the United States, for venous thromboemoblism (VTE) prevention after knee and hip replacement surgery. Rivaroxaban (Xarelto) has been approved for both VTE prevention in the United States and Europe. To date there have been no head-to-head comparisons of the newer anticoagulants.
According to a recent study in Circulation: Cardiovascular Quality and Outcomes, dabigatran now has about 19% of the oral anticoagulant market, mostly for the approved treatment of AF “but increasingly for off-label indications” as well. A recent letter in the Journal of the American College of Cardiology provided information about the off-label use of dabigatran in two mechanical valve patients. Both patients developed thrombosis after switching to dabigatran from warfarin. The authors noted that “while there is a wealth of data and clinical experience on dosing and therapeutic response to warfarin in this context, these data are unavailable for dabigatran.” Although newer anticoagulants “hold tremendous promise for mechanical valve anticoagulation… there is a need for dose-finding studies and clinical trials to demonstrate safety and efficacy in this setting.”
One clinical cardiologist who did not wish to be identified offered the following perspective:
This is similar to the case reports (with all the usual caveats) where we have seen this signal with the novel anticoagulants…. it’s not intuitively clear why this is the case. It may be that the dose is not optimized for mechanical valves. It is worth noting that the drug levels in patients with mechanical valves were lower than anticipated based on pharmacokinetic calculations. Maybe patients with mechanical valves have a different metabolism of the drug versus those that don’t have mechanical valves? There may be an interaction with von Willebrand factor in the pharmacokinetics of dabigatran. Or maybe the dose is just too low and patients with mechanical valves need higher doses, just as we use a higher INR in patients with mechanical valves? The science keeps evolving!
Sanjay Kaul made a similar point:
The anticoagulant dose requirement for mechanical valves is higher even for warfarin (INR targeted for 2.5 to 3.5) compared with atrial fibrillation or VTE indication (Target INR of 2 to 3). It is likely that the dabigatran dose tested in RE-ALIGN was not sufficiently effective early post surgery when the thrombotic risk is the highest.
Click here to read a letter sent by Boehringer Ingelheim to members of its speakers bureau…