Published ATLAS ACS-TIMI 46 results for rivaroxaban pave the way for phase 3 trial

Boston, MA - Results of the phase 2 ATLAS ACS-TIMI 46 trial, which paved the way for the phase 3 ACS trial of rivaroxaban (Xarelto, Johnson & Johnson) now enrolling patients, have now been published online June 17, 2009 in the Lancet ^[1]. First presented at the AHA 2008 meeting (and reported by heartwire at the time), the ATLAS-ACS-TIMI 46 demonstrated that while rivaroxaban, an oral direct factor Xa inhibitor, increased the risk of bleeding in a dose-dependent manner in stabilized ACS patients, it showed promise in reducing major ischemic outcomes, particular in the lower doses studied.

According to first author on the study, Dr Jessica Mega (Brigham and Women's Hospital, Boston, MA), the phase 3 trial, dubbed ATLAS ACS 2-TIMI 51, is already up and running with a target enrollment of up to 16 000 patients.

"[ATLAS-ACS-TIMI 46] was a phase 2 study, and the goal was to select an appropriate dose to be carried forward into the phase 3 study," Mega told heart wire . "We are pleased that we were able to achieve this goal, and the phase 3 study is evaluating 2.5 mg twice a day and 5 mg twice a day—a total daily dose of 5 mg and 10 mg." The point of the phase 2 trial, she emphasized, was to establish this dose for going forward, and the trial was not powered for efficacy. That said, "We observed that lower doses of rivaroxaban tended to reduce major atherothrombotic events."

Rivaroxaban is just one of several potential new oral anticoagulants in development that many hope will pan out as a substitute for warfarin in the setting of venous thromboembolism, in the prevention of stroke in atrial fibrillation patients, and, as in this study, for the treatment of ACS. Warfarin has generally not been used in clinical practice in the setting of ACS, because of the difficulty of keeping patients in the target bleeding range, except for patients in whom warfarin is indicated for other reasons. Rivaroxaban recently won a recommendation for approval from an FDA advisory panel evaluating the agent in the setting of deep vein thrombosis and pulmonary embolism prophylaxis, although the FDA has since asked the drug-maker for more information (although no additional studies) to support this indication.

In an editorial ^[2] accompanying the study, Drs Hitinder S Gurm and Kim Eagle (University of Michigan Cardiovascular Center, Ann Arbor) call the future of rivaroxaban in ACS "difficult to predict," noting "there was no suggestion of benefit in patients receiving dual antiplatelet therapy; robust clinical benefits without major increase in bleeding risk would need to be shown in the ongoing trials before this drug could be integrated into practice." Moreover, rivaroxaban was linked to a two- to fourfold increase in bleeding, particularly in the elderly and patients with renal disease, they observe. "However," they continue, "we should not be completely pessimistic about the future role of this drug in treating patients with acute coronary syndromes. Although estimation of the drug's benefit in secondary prevention on the basis of the results of a dose-finding study would be premature, rivaroxaban could potentially displace parenteral anticoagulants for early management of these syndromes"—an indication that has "not yet been pursued," they note.

Commenting on the study for heart wire , Dr Robert Harrington (Duke Clinical Research Institute, Durham, NC) emphasized that the buzz over ATLAS ACS-TIMI 46 (in spite of missing its primary efficacy end point) stems in part from the promising results for the secondary efficacy end points and even more so from the promise of new anticoagulants generally. "There is this general excitement in the cardiovascular community about finally being able to replace warfarin, with all its challenges, with another orally available anticoagulant that seems to inhibit thrombosis in an effective manner," he said. On top of this are hopes that using anticoagulants either in place of or on top of antiplatelet therapy could yield greater antithrombotic effects than the kinds of incremental benefits seen with new antiplatelet drugs, he added.

Whether the bleeding risks are amply offset by the clinical gains remains to be seen, Harrington added. "If they get the kind of clinical benefit they are anticipating, the incremental increased risk of bleeding they see here might well be worth the tradeoff, but obviously the only way you're going to know that is if you do all the studies and balance one against the other. "

Also commenting for heart wire , Dr Sanjay Kaul (Cedars Sinai Heart Institute, Los Angeles, CA) highlighted the discrepant results in terms of benefit/risk profile in the stratum-one and stratum-two patients. The stratum-two patients, in whom no efficacy benefit was seen, represent the most common antiplatelet regimen for most ACS patients, he noted.

"I would like to caution the authors from overinterpreting the secondary efficacy data (death, MI, or stroke), which appear to favor rivaroxaban," he said, particularly since the primary efficacy data did not reach statistical significance. He also expressed concerns about the twofold increased bleeding seen in the dose chosen for the phase 3 study, given the relatively low-risk group in whom this bleeding rate was seen.

On the positive side, Kaul praised the large number of patients studied in the phase 2 trial (which typically enroll much lower numbers of patients) and the choice of a bleeding end point that "captures clinically relevant bleeding." Perhaps most striking in ATLAS ACS-TIMI 46, given the dashed hopes following the removal of ximelagatran from the market due to hepatic toxicity, there were "no safety concerns with liver adverse events for at least six months, which is somewhat reassuring," Kaul said.

Heartwire from Medscape © 2009 

Cite this: Published ATLAS ACS-TIMI 46 results for rivaroxaban pave the way for phase 3 trial - Medscape - Jun 17, 2009.