Treatment with oral tafamidis at 80 mg/day provided a significantly greater survival benefit than dosing at 20 mg/day in patients with transthyretin amyloid cardiomyopathy in the long-term extension of the landmark ATTR-ACT trial, Thibaud Damy, MD, PhD, reported at the European Society of Cardiology Heart Failure Discoveries virtual meeting.
Dr. Petar M. Seferovic
Moreover, the superior survival benefit achieved by taking four 20-mg capsules of tafamidis (Vyndaqel) once daily – or its more convenient once-daily, single-capsule, 61-mg bioequivalent formulation marketed as Vyndamax – came at no cost in terms of side effects and toxicity, compared with low-dose therapy for this progressive multisystem disease, according to Dr. Damy, professor of cardiology at the University of Paris and head of the French National Referral Center for Cardiac Amyloidosis at Henri Mondor University Hospital, Créteil, France.
“There are no side effects with tafamidis,” he said. “It doesn’t act on any receptors, it just acts on the formation of amyloid fibrils, so there are no side effects at whatever dosage is used. And in ATTR-ACT there was actually a trend towards increased side effects in the placebo group because the amyloidosis is everywhere, so by decreasing the amyloidosis process you improve not only the heart but all the organs, and the patient has a better quality of life.”
ATTR-ACT (Transthyretin Amyloidosis Cardiomyopathy Clinical Trial) was a phase 3, double-blind study in which 441 patients with transthyretin amyloidosis cardiomyopathy (TAC) in 13 countries were randomized to tafamidis at either 80 mg or 20 mg per day or placebo and followed prospectively for 30 months. At 30 months, all-cause mortality was 29.5% in patients who received tafamidis, compared with 42.9% in controls, for a statistically significant and clinically important 30% relative risk reduction, establishing tafamidis as the first disease-modifying therapy for this disease (N Engl J Med. 2018 Sep 13;379[11]:1007-16).
Patients in the 80-mg group had a 20% reduction in the risk of death, compared with the 20-mg group, at 30 months in an analysis adjusted for baseline age, 6-minute walk distance, and N-terminal pro-B-type natriuretic peptide, all of which are known to impact survival in TAC. This between-group survival difference wasn’t statistically significant, providing one impetus for the subsequent long-term extension study, in which patients remained on their original dose of tafamidis, and the controls who’d been on placebo for 30 months were randomized 2:1 to tafamidis at 80 mg or 20 mg per day.
The primary endpoint in the long-term extension was a composite of all-cause mortality, heart transplantation, or implantation of a ventricular assist device. At a median follow-up of 39 months since ATTR-ACT began, the high-dose tafamidis group had an adjusted 33% reduction in the risk of this endpoint, compared with patients on 20 mg per day, a difference that barely missed statistical significance. At that point, everyone in the long-term extension was switched to the once-daily 61-mg formulation of tafamidis free acid, which is bioequivalent to four 20-mg capsules of tafamidis.
Dr. Damy’s key message: At a median of 51 months of follow-up, the group originally on 80 mg of tafamidis displayed a highly significant adjusted 43% reduction in risk of the composite endpoint, compared with those who had been on 20 mg per day.
Session chair Petar M. Seferovic, MD, PhD, pronounced the ATTR-ACT trial and its long-term extension “a breakthrough advancement.”
“This is the first time in human medical history that we have a drug which improves the long-term outcome, including survival, in patients with this form of hypertrophic cardiomyopathy. So this is extremely important. It’s one of the major steps forward in the treatment of patients with myocardial disease,” said Dr. Seferovic, president of the European Society of Cardiology Heart Failure Association and professor of internal medicine at the University of Belgrade, Serbia.
Discussant Loreena Hill, PhD, of Queen’s University in Belfast, Northern Ireland, observed that TAC is a devastating disease with a formidable symptom burden and an average survival of just 2-5 years after diagnosis.
“It is often underdiagnosed, and yet it is estimated to account for up to 13% of patients with heart failure and preserved ejection fraction,” she said, adding that she considers the long-term extension results “extremely positive.”