Efficacy and safety of once-weekly somatrogon following up to 4 years of treatment in Japanese children with growth hormone deficiency: results from an open-label extension of a phase 3 study.

Somatrogon is a long-acting recombinant human growth hormone approved in several countries, including Japan, for the treatment of children with growth hormone deficiency (GHD). In this study (Clinicaltrials.gov:NCT03874013) Japanese patients with GHD initially received once-weekly somatrogon or once-daily somatropin (0.175 mg/kg/week) for 12 months in the main study period; those who completed the main study were eligible to enroll in a single-arm, 3-year open-label extension (OLE) and receive once-weekly somatrogon (0.66 mg/kg/week). The primary endpoints of the OLE included annualized height velocity (HV), change in height standard deviation score (SDS), and safety. Of 43 patients who completed the main study, 42 continued into the OLE and 40 completed the OLE. Patients were analyzed by treatment received (somatrogon vs. somatropin) during the main study. Mean (SD) HV at OLE baseline was higher in patients originally randomized to somatrogon vs. somatropin (9.78 [1.59] vs. 7.70 [1.10] cm/year); mean HV was similar between original treatment groups for all other OLE timepoints. Mean height SDS increased from main study baseline through the end of the OLE in both treatment groups. During the OLE, 22 (100%) somatrogon-treated patients and 18 (90%) somatropin-treated patients reported treatment-emergent adverse events (TEAEs). Most TEAEs were mild or moderate in severity and no patients discontinued from the OLE or required dose reductions due to TEAEs. Up to 4 years of treatment with once-weekly somatrogon resulted in improved growth response and was well tolerated in Japanese patients with pediatric GHD, including patients who switched to somatrogon from once-daily somatropin.Clinialtrials.gov:NCT03874013.