Pharmacokinetics and Pharmacodynamics of Macimorelin Acetate (AEZS-130) in Paediatric Patients With Suspected Growth Hormone Deficiency (GHD)

Growth hormone deficiency (GHD) in children is a rare, aetiologically diverse condition that results in growth failure and short stature. Inadequate response to two different growth hormone stimulation tests (GHST) is required for the diagnosis of GHD. Macimorelin acetate, a potent, orally administered growth hormone (GH) secretagogue, is approved by the FDA and EMA for the diagnosis of adult GHD. Study AEZS-130-P01 is the first of two studies to investigate macimorelin acetate as a diagnostic test in children with suspected GHD. This was an open-label, group comparison, dose escalation trial to investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of single-dose 0.25, 0.5 and 1 mg/kg oral macimorelin acetate in paediatric subjects with suspected GHD. The macimorelin GHST was administered between two standard GHST, conducted as per local clinical practice, with a recovery period of 7-28 days between tests. Blood samples were collected pre-dose (±15 min) and 15, 30, 45, 60, 90, 120 and 360 minutes after macimorelin acetate intake. Overall, 24 paediatric subjects (8 per cohort [C1, C2, C3]) were included in the pharmacokinetic/pharmacodynamic (PK/PD) analysis. Five males and 3 females were observed in C1 and C2, 7 males and 1 female in C3. In all three cohorts, at least 3 subjects represented Tanner stages I or II. All 24 subjects (100%) were white, with a median age of 9.8, 9.0 and 10.5 years (range 4-15 years) and a median body-mass index of 16.1 kg/m2 (12.4-21.4 kg/m2) at screening. Overall, 88 adverse events were reported, many related to the standard GHST; none were considered related to the macimorelin test. Maximum plasma concentrations for macimorelin were mainly observed between 30-45 min. The mean Cmax values were 3.46, 8.13 and 12.87 ng/ml for C1, C2, and C3, respectively. The AUCs increased with dose; the mean AUC0-6 values were 6.69, 18.02 and 30.92 h*ng/mL. The mean elimination half-lives were 1.22, 1.61 and 1.71 h, respectively. PK and PD profiles for all three cohorts were comparable, with peak GH levels mainly observed within 30-60 min following macimorelin intake. Macimorelin acetate was safe and well tolerated in all dosing cohorts. A dose-dependent increase in macimorelin Cmax and AUC in children and adolescents correlated well with data from adult subjects. A robust dose-proportional GH response was also achieved. PD results showed that GH response was comparable in all dose groups, with a slight shift to earlier tmax at higher macimorelin doses.