Efficacy and safety of tafamidis doses in the Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT) and long-term extension study

Aims: Tafamidis is an effective treatment for transthyretin amyloid cardiomyopathy (ATTR-CM) in the Tafamidis in Transthyretin Cardiomyopathy Clinical Trial (ATTR-ACT). While ATTR-ACT was not designed for a dose-specific assessment, further analysis from ATTR-ACT and its long-term extension study (LTE) can guide determination of the optimal dose.

Methods and results: In ATTR-ACT, patients were randomized (2:1:2) to tafamidis 80 mg, 20 mg, or placebo for 30 months. Patients completing ATTR-ACT could enrol in the LTE (with placebo-treated patients randomized to tafamidis 80 or 20 mg; 2:1) and all patients were subsequently switched to high-dose tafamidis. All-cause mortality was assessed in ATTR-ACT combined with the LTE (median follow-up 51 months). In ATTR-ACT, the combination of all-cause mortality and cardiovascular-related hospitalizations over 30 months was significantly reduced with tafamidis 80 mg (P = 0.0030) and 20 mg (P = 0.0048) vs. placebo. All-cause mortality vs. placebo was reduced with tafamidis 80 mg [Cox hazards model (95% confidence interval): 0.690 (0.487-0.979), P = 0.0378] and 20 mg [0.715 (0.450-1.137), P = 0.1564]. The mean (standard error) change in N-terminal pro-B-type natriuretic peptide from baseline to Month 30 was -1170.51 (587.31) (P = 0.0468) with tafamidis 80 vs. 20 mg. In ATTR-ACT combined with the LTE there was a significantly greater survival benefit with tafamidis 80 vs. 20 mg [0.700 (0.501-0.979), P = 0.0374]. Incidence of adverse events in both tafamidis doses were comparable to placebo.

Conclusion: Tafamidis, both 80 and 20 mg, effectively reduced mortality and cardiovascular-related hospitalizations in patients with ATTR-CM. The longer-term survival data and the lack of dose-related safety concerns support tafamidis 80 mg as the optimal dose.

Clinical trial registration: ClinicalTrials.gov NCT01994889; NCT02791230.