Average IGF-1 Prediction for Once-Weekly Lonapegsomatropin in Children With Growth Hormone Deficiency

Context Serum insulin-like growth factor 1 (IGF-1) levels are relatively constant in somatropin-treated children with growth hormone deficiency (GHD), and guide dose adjustments for clinical efficacy and long-term safety. IGF-1 levels following treatment with long-acting growth hormones such as lonapegsomatropin (lonapegsomatropin-tcgd, TransCon hGH), a once-weekly somatropin prodrug, exhibit a characteristic profile over the dosing interval. Objective This study aimed to develop a method to predict average IGF-1 in lonapegsomatropin-treated GHD children to interpret IGF-1 data based on a single sample obtained any time at steady state. Methods A population nonlinear mixed-effect pharmacodynamic model for IGF-1 was developed based on 2 randomized, open-label trials of TransCon hGh in GHD children and used to develop a linear mixed model with Taylor series to fit simulated IGF-1 profiles of lonapegsomatropin-treated children. A total of 49 896 IGF-1 sample data simulated from 105 lonapegsomatropin-treated GHD children were utilized for the final prediction model. The dosage range of TransCon hGh was 0.14 to 0.30 hGH mg/kg/week, and weekly average IGF-1 was calculated using IGF-1 profiles simulated from the nonlinear pharmacodynamic model. Predicted average IGF-1 was obtained by linear mixed model with Taylor series. Results The nonlinear mixed-effect model provided satisfactory model fit. The linear mixed model with Taylor series fit simulated IGF-1 data well, with a relatively straightforward prediction formula. IGF-1 values sampled at ~4.5 days post-dose coincided with weekly average IGF-1 at steady state. Conclusion A formula to predict average IGF-1 from a single sample of IGF-1 at steady state was established to aid clinicians in interpreting IGF-1 levels in GHD children administered lonapegsomatropin.