BACKGROUND: Mineralocorticoid receptor antagonists (MRA) improve outcomes in patients with heart failure and reduced ejection fraction (HFrEF) but are underused in clinical practice. Observational data suggest that hyperkalemia is the leading obstacle for the suboptimal use of MRA. OBJECTIVES: This study sought to evaluate the effects of sodium zirconium cyclosilicate (SZC) in optimizing use of spironolactone among participants with HFrEF and hyperkalemia. METHODS: REALIZE-K (Study to Assess Efficacy and Safety of SZC for the Management of High Potassium in Patients With Symptomatic HFrEF Receiving Spironolactone) was a prospective, double-blind, randomized- withdrawal trial in participants with HFrEF (NYHA functional class II-IV; left ventricular ejection fraction ≤40%), optimal guideline-directed therapy (except MRA), and prevalent or incident MRA-induced hyperkalemia. During open-label run-in, participants underwent spironolactone titration (target: 50 mg/day); those with hyperkalemia started SZC. Participants with normokalemia (potassium: 3.5-5.0 mEq/L) on SZC and spironolactone ≥25 mg/day were randomized to continued SZC or placebo for 6 months. The primary endpoint was optimal treatment response (normokalemia on spironolactone ≥25 mg/day without rescue therapy for hyperkalemia [months 1-6]). The 5 secondary endpoints were tested hierarchically. Exploratory endpoints included a composite of adjudicated cardiovascular death or worsening heart failure (HF) events (hospitalizations and urgent visits). RESULTS: Overall, 203 participants were randomized (SZC: 102; placebo: 101). Higher percentage of SZC- vs placebo-treated participants had optimal response (71% vs 36%; OR: 4.45; 95% CI: 2.89-6.86; P < 0.001). SZC (vs placebo) improved the first 4 secondary endpoints: normokalemia on randomization dose of spironolactone and without rescue therapy (58% vs 23%; OR: 4.58; 95% CI: 2.78-7.55; P < 0.001); receiving spironolactone ≥25 mg/day (81% vs 50%; OR: 4.33; 95% CI: 2.50-7.52; P < 0.001); time to hyperkalemia (HR: 0.51; 95% CI: 0.37-0.71; P < 0.001); and time to decrease/discontinuation of spironolactone due to hyperkalemia (HR: 0.37; 95% CI: 0.17-0.73; P = 0.006). There was no between-group difference in Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score at 6 months (-1.01 points; 95% CI: -6.64 to 4.63; P = 0.72). Adverse events (64% vs 63%) and serious adverse events (23% vs 22%) were balanced between SZC and placebo, respectively. Composite of cardiovascular (CV) death or worsening HF occurred in 11 (11%) participants in the SZC group (1 with CV death, 10 with HF events) and 3 (3%) participants in the placebo group (1 with CV death, 2 with HF events; log-rank nominal P = 0.034). CONCLUSIONS: In participants with HFrEF and hyperkalemia, SZC led to large improvements in the percentage of participants with normokalemia while on optimal spironolactone dose, and reduced risk of hyperkalemia and down-titration/discontinuation of spironolactone. Although underpowered for clinical outcomes, more participants had HF events with SZC than placebo, which should be factored into the clinical decision making. (Study to Assess Efficacy and Safety of SZC for the Management of High Potassium in Patients With Symptomatic HFrEF Receiving Spironolactone; NCT04676646).

BioPharmaceuticals Medical AstraZeneca Cambridge United Kingdom

BioPharmaceuticals Medical AstraZeneca Gothenburg Sweden

BioPharmaceuticals Medical AstraZeneca Wilmington Delaware USA

Cardiovascular Division Brigham and Women's Hospital Boston Massachusetts USA

Department of Electrocardiology Medical University of Lodz Łódź Poland

Fortrea Maidenhead Surrey United Kingdom

Hospital Clinico Universitario de Valencia and University of Valencia Valencia Spain

Hospital Clínico Universitario de Valencia University of Valencia Valencia Spain

Hospital Israelita Albert Einstein São Paulo Brazil

Hospital Universitario Puerta de Hierro Majadahonda Madrid Spain

Hospital Universitário São Francisco de Assis na Providência de Deus and Universidade São Francisco Bragança Paulista Brazil

Icahn School of Medicine Mount Sinai Fuster Heart Hospital New York New York USA

Institute of Cardiovascular and Medical Sciences University of Glasgow and Glasgow Royal Infirmary Glasgow United Kingdom

Institute of Unity Health Toronto and University of Toronto Toronto Ontario Canada

Keenan Research Centre for Biomedical Science Unity Health Division Head Cardiology St Michael's Hospital Toronto Ontario Canada

NIHR Cardiovascular Biomedical Research Unit Glenfield Hospital Leicester United Kingdom

Saint Luke's Mid America Heart Institute and University of Missouri Kansas City Kansas City Missouri USA

Section of Cardiovascular Medicine Yale University Guilford Connecticut USA

Semmelweis University Budapest Hungary

University Health Network and Mount Sinai Hospital and University of Toronto Toronto Ontario Canada

University Hospital Ostrava and Faculty of Medicine University of Ostrava Czech Republic

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NCT04676646