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Background and Importance Sodium zirconium cyclosilicate (SZC) is authorised for the treatment of chronic hyperkalaemia in adult patients. In October 2024, the Pharmacy and Therapeutics Committee at our centre approved its use for acute hyperkalaemia in emergency situations, in patients already receiving standard hyperkalaemia treatment who met the following criteria: serum potassium >6.5 mmol/L, electrocardiographic changes, and intolerance to ion-exchange resins.Aim and Objectives To evaluate the conditions of use and effectiveness of SZC as an off-label treatment in acute severe hyperkalaemia.Material and Methods Retrospective observational study including adult patients treated with SZC from October 2024 to May 2025 in a tertiary hospital. Data were collected through the electronic prescription registry and the electronic medical record system.Demographic, clinical, laboratory, and pharmacotherapeutic variables were collected, including prior treatment with hypokalaemic agents (calcium gluconate, insulin and intravenous glucose) and whether the use of ion-exchange resins was considered inadequate. Effectiveness was measured as serum potassium reduction in 24 hours.Continuous variables were expressed as median (interquartile range) and categorical variables as absolute number of cases (percentages).Results Thirteen patients were included, all with acute hyperkalaemia secondary to renal failure. The median age was 64 years, and 11 (84.6%) were male.Two patients (15.4%) met the criterion of serum potassium > 6.5 mmol/L, and six patients (46.1%) presented electrocardiographic changes due to hyperkalaemia. Regarding prior treatments, nine patients (69.2%) had received calcium gluconate and eight (61.5%) insulin and intravenous glucose.Median serum potassium levels were 6.1 mmol/L before SCZ treatment and 5.26 after 24 hours, with a median decrease of 0.79 mmol/L (IQR: 0.7). A patient was excluded from the effectiveness analysis due to death before the time of evaluation.Conclusion and Relevance Some patients did not fully meet the approved prescription criteria at our centre, indicating suboptimal adherence to established guidelines and a tendency toward early treatment initiation.SZC appears to be an effective adjunctive treatment for acute severe hyperkalaemia in patients with renal failure who are already receiving standard therapy, achieving near- normalisation of serum potassium within 24 hours.Conflict of Interest No conflict of interest