Objective: Somapacitan is a reversible albumin-binding growth hormone (GH) derivative, developed for once-weekly administration. This study aimed to evaluate the safety of once-weekly somapacitan vs once-daily Norditropin^®. Local tolerability and treatment satisfaction were also assessed.

Design: 26-week randomized, controlled phase 3 safety and tolerability trial in six countries (Nbib2382939).

Methods: Male or female patients aged 18-79 years with adult GH deficiency (AGHD), treated with once-daily GH for ≥6 months, were randomized to once-weekly somapacitan (n = 61) or once-daily Norditropin (n = 31) administered subcutaneously by pen. Both treatments were dose titrated for 8 weeks to achieve insulin-like growth factor I (IGF-I) standard deviation score (SDS) levels within the normal range, and then administered at a fixed dose. Outcome measures were adverse events (AEs), including injection site reactions; occurrence of anti-somapacitan/anti-GH antibodies and change in treatment satisfaction, assessed using the Treatment Satisfaction Questionnaire for Medication-9 (TSQM-9).

Results: Mean IGF-I SDS remained between 0 and 2 SDS throughout the trial in both groups. AEs were mostly mild or moderate and transient in nature. The most common AEs were nasopharyngitis, headache and fatigue in both groups. More than 1500 somapacitan injections were administered and no clinically significant injection site reactions were reported. No anti-somapacitan or anti-GH antibodies were detected. The TSQM-9 score for convenience increased significantly more with somapacitan vs Norditropin (P = 0.0171).

Conclusions: In this 26-week trial in patients with AGHD, somapacitan was well tolerated and no safety issues were identified. Once-weekly somapacitan was reported to be more convenient than once-daily Norditropin.