Abstract BACKGROUND AND AIMS Continuous erythropoietin receptor activator—methoxy polyethylene glycol epoetin beta (C.E.R.A.) is a long-acting erythropoiesis-stimulating agent (ESA) approved for the treatment of anaemia associated with chronic kidney disease (CKD) in adults. In June 2018, the Food and Drug Administration approved the use of C.E.R.A. administered intravenously in patients on haemodialysis aged 5–<18 years switching from another ESA. This observational real-world study (MH40258) assessed the safety, dosing and haemoglobin (Hb) levels associated with C.E.R.A. in paediatric patients with CKD on dialysis. METHOD This was a non-interventional real-world study of patients from the International Paediatric Peritoneal Dialysis Network (IPPN) and the International Paediatric Hemodialysis Network (IPHN) registries. Demographics, clinical characteristics, dialysis information, treatment, laboratory parameters, number and causes of hospitalization events and deaths were reported in patients treated with C.E.R.A. from both registries (IPPN: 2007–2021; IPHN: 2013–2021). RESULTS Overall, 229 patients had at least one observation while being treated with C.E.R.A. and were analysed in this study; 177 on peritoneal dialysis (PD) (median age 10.6 years, interquartile range [IQR] 4.2–14.6) and 52 on haemodialysis (HD) (median age 14.1 years, IQR 10.4-16.2). The median observation time under C.E.R.A. exposure was 6 months (IQR 0–12.5) for PD patients and 12 months (0–18) for HD patients. 121 PD patients (68%) and 36 HD patients (69%) had ≥ 1 hospitalization, of whom 102/121 (84%) and 32/36 (89%), respectively, had non-elective hospitalizations. Median hospitalization surveillance time/patient was 13.5 months in the PD and 18.3 months in the HD cohorts. The most frequent causes for non-elective hospitalization were infections, reported as a cause in 56/177 (32%) patients in the PD cohort and 14/52 (27%) in the HD cohort and technique complications, in 41/177 (23%) patients in the PD cohort and 20/52 (38%) in the HD cohort. There were seven deaths (PD: 5 patients; HD: 2 patients), corresponding to an overall mortality rate of 19.8 cases per 1000 observation years. Causes of death were infections (n = 2), intracranial bleeding (n = 2), congestive heart failure (n = 2) and one case of sudden death at home. Hb levels remained stable over time with 47% of PD patients and 48% of HD patients having a Hb value within the range of 10–12 g/dL at their last observation. Mean [standard deviation (SD)] Hb levels at last observation were 10.9 (1.7) g/dL in the PD and 10.4 (1.7) g/dL in the HD cohort. The median monthly dose of C.E.R.A. at first visit was 100 (IQR 50–120) µg in the PD and 107 (80–129) µg in the HD cohort, while at last visit it was 100 (50–150) µg (PD) and 80 (54–129) µg (HD). While absolute C.E.R.A. dose increased with age, weight-related doses decreased substantially with age in both cohorts: in groups aged < 2, 2–<5, 5–<12 and 12–<18 years, respectively, the median monthly dose was 7.9, 5.4, 3.2 and 2.6 µg/kg at first observation and 5.1, 5.2, 3.0 and 3.0 µg/kg at last observation in the PD cohort. The age-related dosing differences were smaller when doses were normalized to body surface area (BSA) rather than body weight, with median doses at last visit of 114, 121, 87 and 98 µg/m2/month, respectively in the PD cohort. In the HD cohort, a similar pattern wasobserved regarding weight and BSA-based dosing, but overall C.E.R.A.dosing was generally lower over the course of the study in HD compared with PD patients. The median monthly C.E.R.A. dose at last observation was 3.5 (IQR 2.3– 5.1) µg/kg, or 95 (62–145) µg/m2 in the PD cohort and 2.1 (1.2–3.4) µg/kg, or 63 (40–98) µg/m2 in the HD cohort (Table). CONCLUSION Real-world data from the IPPN and IPHN registries indicated that C.E.R.A. treatment is associated with efficient maintenance of Hb levels in paediatric patients with CKD on dialysis. C.E.R.A. appeared to have a favourable safety profile; analysis of hospitalization rate and causes as well as patient mortality did not reveal any safety signals.