The effect of <scp>LysaKare</scp> infusion on serum potassium levels in patients with gastroenteropancreatic neuroendocrine tumours eligible for treatment with [ <scp> ¹⁷⁷ Lu </scp> ]Lu‐ <scp>DOTA</scp> ‐ <scp>TATE</scp> : A post‐authorisa

Lu-DOTATATE treatment received 1000 mL of LysaKare (monotherapy) intravenously over 4 h. The primary endpoint was the change in serum potassium levels over the course of 24 h. Secondary endpoints included the incidence of LysaKare-related adverse events (AEs) and changes in laboratory parameters. Forty-one patients were treated (median age, 57 years; 92.7% White and 7.3% Black; 53.7% male) and 40 completed post-treatment follow-up. Mean (standard deviation [SD]) serum potassium was 4.33 (0.397) mmol/L pre-dose, increasing by 0.60 (0.666) mmol/L after 4 h (time to maximum change, range, 2-24 h) before decreasing to around the pre-dose level: the mean (SD) increase after 24 h was 0.07 (0.396) mmol/L. Other electrolytes and blood gas components mostly showed transient changes that lasted ~24 h. A general trend of transient metabolic acidosis was also observed based on laboratory values. Serum potassium grade increased from baseline in 41.5% of patients. By comparison, five patients (12.2%) had a treatment-related AE of hyperkalaemia (grade 3, n = 1); all resolved within 24 h, either without treatment (n = 3) or following intravenous furosemide (n = 2). There were no serious AEs and no AEs leading to treatment discontinuation/interruption. This PASS identified no new safety signals attributable to LysaKare. Trial registration: EudraCT, 2019-004073-76. Registered 20/08/2020.