Review of variation in IGF-1 concentrations between different formulations of growth hormone replacement therapy in adults with growth hormone deficiency — ASN Events
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Review of variation in IGF-1 concentrations between different formulations of growth hormone replacement therapy in adults with growth hormone deficiency (#367)

Aisling Miller 1 2 , Jane Sorbello 3 , Amber Achille 3 , Raquel Maggacis 2 3 , Jack Lockett 2 3 , Brendan Nolan 3 4 , Warrick Inder 5
  1. Princess Alexandra Hospital, Mount Gravatt, QLD, Australia
  2. PA-Southside Clinical Unit, University of Queensland, Brisbane, Queensland, Australia
  3. Department of Diabetes and Endocrinology, Princess Alexandra Hospital, Brisbane, Queensland, Australia
  4. University of Melbourne, Melbourne, Victoria, Australia
  5. University of Queensland, Brisbane, Queensland, Australia

Growth hormone (GH) replacement therapy (somatropin) is subsidised by the Pharmaceutical Benefit Scheme in Australia for adults with defined criteria for GH deficiency. Dose titration is primarily achieved through monitoring of serum insulin-like growth factor 1 (IGF-1) levels, with symptoms also guiding dosing. Multiple brands of somatropin are available within Australia that are assumed equipotent. Due to medication supply issues since 2020, it had often been necessary for patients to swap between different formulations. This study sought to assess for variation in IGF-1 levels and somatropin doses after switching somatropin formulations.

This is a retrospective quantitative analysis of data from a single institution between 2023-2025. Patients were identified from the prescription and pharmacy database of the Princess Alexandra Hospital endocrinology department, a quaternary centre in Queensland. The primary endpoint was change in IGF-1 concentration after swapping between GH formulations. The secondary endpoint was to assess for a dose change requirement post GH formulation switch. Changes in IGF-1 parameters relative to the reference range midpoint from before and after formulation switch were analysed using paired t tests or Wilcoxon signed rank tests. Change in IGF-1 concentration was analysed using linear mixed effect models. 

Fifty-two patients on GH replacement therapy were identified as having been prescribed two different somatropin formulations and included. The most common formulation switches were Norditropin to Genotropin (38.5%) and Genotropin to Saizen (23.1%).  No statistically significant changes were observed in any IGF-1 parameter following GHR brand switching. There was no statistically significant correlation between time interval between switch and IGF-1 measurement, and magnitude of IGF-1 change. Ten patients (19.2%) required a dose increase following formulation switch, with no significant difference between switch combinations. 

Switching between different formulations of somatropin did not lead to significant variation in IGF-1 levels or dose change requirements.