Metabolic and muscular effects of switching from somatropin to somapacitan in adults with growth hormone deficiency

Context Once-weekly somapacitan is approved for treating adults with growth hormone deficiency. Phase 3 trials support its non-inferiority to daily growth hormone (GH); however, its effect on comprehensive metabolic outcome, including muscle strength, during routine care, remains unclear. Objective To compare the metabolic and functional outcomes in patients who switched from daily GH to somapacitan with those who continued daily GH. Design Prospective, observational, non-randomized comparative study conducted from baseline to 52 weeks. Setting A single-center providing routine endocrine management. Patients Fifty-seven adults on growth hormone replacement therapy were self-selected to receive either once-weekly or continued daily GH. Intervention Switching from daily GH to once-weekly somapacitan, or continuing daily treatment based on patient preference. Main Outcome Measures The prespecified primary endpoint was the dual-energy x-ray absorptiometry-derived change in total lean mass from baseline to week 52. Exploratory endpoints included body composition, lipid profile, and physical performance. Results Baseline and week 52 insulin-like growth factor 1 standard deviation scores distributions were similar between the groups; yet the increase was greater with daily GH than with somapacitan. The primary endpoint showed no between-group difference (mean difference −0.2 kg; 95% CI -1.5 to 1.1). Somapacitan was associated with increased adiposity indices, yet it improved high-density lipoprotein-cholesterol. Exploratory analyses revealed improvements in handgrip strength and Timed Up and Go Test. No new safety concerns were observed. Conclusions In routine practice, switching to once-weekly somapacitan was associated with improved functional outcomes, despite less favorable adiposity trajectories, compared with daily therapy. Further studies are required to clarify long-term effects.