Extension of the Phase 3 Trial of Somatrogon in Children with Growth Hormone Deficiency: 3 Years of Safety and Efficacy

INTRODUCTION: Somatrogon is a once-weekly, long-acting growth hormone approved to treat children with growth hormone deficiency (GHD). This study evaluated the long-term efficacy and safety of once-weekly somatrogon in children with GHD following up to 3 years of treatment. METHODS: During the 12-month main study, patients were randomized 1:1 to once-weekly somatrogon (0.66 mg/kg/week) or once-daily somatropin (0.24 mg/kg/week). Patients could then enter an open-label extension (OLE), wherein somatrogon-treated patients continued receiving somatrogon and somatropin-treated patients switched to somatrogon (0.66 mg/kg/week). Data to the end of the second year of the OLE (OLE year [Y] 2) are reported. Of the 222 patients who completed the main study, 212 entered OLE Y1 and 177 entered OLE Y2. RESULTS: Mean (SD) height velocity (HV) was 8.11 (1.84) and 7.91 (1.84) cm/year at OLE Y1 and Y2, respectively. Mean (SD) height SD score (SDS) was -1.42 (0.90) and -0.95 (0.84) in OLE Y1 and Y2, respectively. In OLE Y1 and Y2, mean change in height SDS (ΔHSDS) was 1.36 and 1.61, respectively, and mean insulin-like growth factor I (IGF-I) SDS remained >1, confirming the efficacy of the treatment. Patients who switched from somatropin to somatrogon had similar HV, height SDS, and ΔHSDS to those who received somatrogon continuously. The incidence of adverse events (all causality) was 71.7% and 72.3% in OLE Y1 and Y2, respectively; most were mild or moderate in severity. Injection site pain and injection site erythema were the most commonly reported treatment-related adverse events in the OLE period. In OLE Y1 and Y2, up to one quarter of patients had IGF-I SDS >2 at two consecutive assessments, meeting protocol criteria for dose reduction. CONCLUSION: Following up to 3 years of somatrogon treatment, children with GHD showed a persistent increase in linear growth velocity compared to baseline. Somatrogon was well tolerated, with no new safety signals identified.