AIM: Serelaxin is a recombinant human relaxin-2 hormone, which confers receptor-mediated vasodilatation in a tissue-specific fashion. The RELAX-AHF-EU study assessed the effect of serelaxin when added to standard-of-care (SoC) therapy on worsening heart failure (WHF)/all-cause death through Day 5 in patients hospitalised for acute heart failure (AHF) in Europe.

METHODS AND RESULTS: This multicentre, prospective, randomised, open-label, blinded-endpoint validation study enrolled hospitalised AHF patients and randomised (2:1) eligible patients (mild-to-moderate renal impairment and systolic blood pressure ≥ 125 mmHg) within 16 h of presentation with signs/symptoms of AHF, to receive 48 h intravenous infusion of 30 μg/kg/day serelaxin + SoC or SoC alone. The primary endpoint was adjudicated WHF/all-cause death through Day 5. Of 3183 patients targeted, 2666 were randomised when the study was terminated early by the sponsor due to the neutral results of the pivotal RELAX-AHF-2 study. Adjudicated WHF/all-cause death through Day 5 was significantly reduced in the serelaxin + SoC vs. SoC group (5.0% vs. 6.9%; hazard ratio 0.71; 95% confidence interval 0.51-0.98; P = 0.0172) (absolute risk reduction 1.9%, number needed to treat 53). The difference between treatment groups was not significant for WHF/all-cause death/heart failure rehospitalisation through Day 14 and length of hospital stay. A significantly smaller proportion of patients in the serelaxin + SoC vs. SoC group experienced persistent heart failure signs/symptoms at each visit until Day 4, or renal deterioration through Day 5 (all P ≤ 0.01). Overall incidence of treatment-emergent adverse events was comparable between treatment groups. Hypotension and decrease in haemoglobin/haematocrit were more frequent in the serelaxin + SoC group.

CONCLUSION: When added to SoC, serelaxin reduced adjudicated WHF or all-cause death through Day 5 in AHF patients. The results from this open-label study should be considered in the context of the totality of the double-blind, randomised evidence on serelaxin in AHF.