Background/Aims: MOD-4023 is a long-acting human growth hormone (hGH) in clinical trials for the treatment of growth hormone deficiency (GHD). A key goal is maintenance of serum concentrations of insulin-like growth factor (IGF) 1 within normal range throughout GH dosing. The study aimed to develop a pharmacokinetic model for MOD-4023 and a pharmacodynamic model for the effect of MOD-4023 on IGF-1 to allow estimation of peak and mean IGF-1 and to identify the optimal IGF-1 sampling day. Methods: MOD-4023 (0.25, 0.48, or 0.66 mg/kg) was administered weekly for 12 months to 41 GH-naive GHD children (age 3–11 years). The control group (n = 11, age 4–9 years) received daily recombinant human growth hormone (r-hGH; 34 µg/kg). Sparse samples (4/subject) were obtained to determine serum concentrations of MOD-4023 or r-hGH and IGF-1. Results: A 2-compartment pharmacokinetic model with first-order absorption fit MOD-4023 data well; a 1-compartment model was appropriate for r-hGH. For both, weight-normalized systemic parameters were preferred over allometric scaling. For MOD-4023, an indirect model fit IGF-1 SDS data well; baseline IGF-1 increased over time. At steady state, samples obtained 4 days following dose administration predicted mean IGF-1 SDS during the dosing interval well. Conclusion: The IGF-1 profile is consistent with the weekly dosing interval. Sampling 4 days following dose administration allows estimation of mean IGF-1 SDS during the dosing interval in GHD patients.
