(somatrogon-ghla)
Somatrogon-ghla binds to the GH receptor and initiates a signal transduction cascade culminating in changes in growth and metabolism. Somatrogon-ghla binding leads to activation of the STAT5b signaling pathway and increases the serum concentration of Insulin-like Growth Factor (IGF-1). GH and IGF-1 stimulate metabolic changes, linear growth, and enhance growth velocity in pediatric patients with GHD.
Following single dose administration of somatrogon, dose-dependent increases in IGF-1 response were observed.
Following multiple dosing, IGF-1 SDS levels were in the normal range for pediatric patients with GHD, similar to daily somatropin. IGF-1 levels peak approximately 2 days (48 hours) post-dose, with the average weekly IGF-1 occurring approximately 4 days post-dose.
Somatrogon-ghla pharmacokinetics (PK) was assessed using a population PK approach for NGENLA in 151 pediatric patients (aged 3 to 15.5 years) with GHD.
Absorption
Following subcutaneous injection, serum concentrations increased slowly, peaking 6 to 25 hours with a median of 11 hours after dosing.
In pediatric patients with GHD, somatrogon-ghla exposure increases in a dose-proportional manner for doses of 0.25 mg/kg/wk, 0.48 mg/kg/wk, and 0.66 mg/kg/wk. There is no accumulation of somatrogon-ghla after once weekly administration. In pediatric patients with GHD, the mean population PK estimated steady-state peak concentrations (mean ± SD) following 0.66 mg/kg/wk was 495 ± 90 ng/mL.
Distribution
In pediatric patients with GHD, the mean population PK estimated apparent central volume of distribution was 0.342 L/kg and apparent peripheral volume of distribution was 0.671 L/kg.
Elimination
In pediatric patients with GHD, the mean population PK estimated apparent clearance was 0.0398 L/h/kg. The mean population PK estimated effective half-life was 37.7 hours, which allows for weekly dosing. Somatrogon-ghla will be present in the circulation for about 8 days after the last dose.
Specific Populations
Based on population PK analyses, age, sex, race, and ethnicity do not have a clinically meaningful effect on the pharmacokinetics of somatrogon-ghla in pediatric patients with GHD. The exposure of somatrogon-ghla decreases with an increase in body weight. However, the somatrogon-ghla dosing regimen of 0.66 mg/kg/wk provides adequate systemic exposure over the body weight range of 10 to 54 kg evaluated in the clinical studies.
The observed incidence of anti-drug antibodies is highly dependent on the sensitivity and specificity of the assay. Differences in assay methods preclude meaningful comparisons of the incidence of anti-drug antibodies in the studies described below with the incidence of anti-drug antibodies in other studies, including those of somatrogon or other growth hormone products.
During the 12-month main period of study NCT 02968004, 84/109 (77.1%) of somatrogon-ghla‑treated patients tested positive for anti-drug antibodies, with most showing specificity to human growth hormone. The anti-drug antibodies persisted in most of the subjects during the study. Neutralizing antibodies developed in 8/217 (3.7%) of somatrogon-ghla-treated patients during the study for up to 42 months of exposure to somatrogon-ghla. The neutralizing antibodies were transient in all subjects. Anti-drug antibodies, including neutralizing-antibodies, did not appear to have a clinically significant impact on the safety or effectiveness of NGENLA during the 12‑month randomized treatment period. Additionally, no apparent effect of anti-drug antibodies on growth was observed for additional 30 months of exposure to somatrogon-ghla in the uncontrolled extension period of study NCT 02968004.
Anti-Drug Antibody Effects on Pharmacokinetics
The population pharmacokinetic analysis of data from study NCT 02968004 showed that patients who tested positive for anti-drug antibodies had an approximately 26% decrease in apparent clearance. These anti-drug antibody-associated pharmacokinetic changes are not considered to be clinically significant.
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