Safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in healthy adults: Results of a single-dose, randomized controlled study

Objective Macimorelin is an orally active ghrelin receptor agonist indicated for the diagnosis of adult growth hormone (GH) deficiency in the United States. This phase 1 study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending doses of macimorelin (including a supratherapeutic dose to be used in a thorough QT trial) in healthy adults. Design Participants were randomized to receive macimorelin 0.5, 1.0, or 2.0 mg/kg or placebo in 1 of 3 sequential ascending-dose cohorts. Blood samples for pharmacokinetic and pharmacodynamic assays were collected pre-dose and at specified time points over a 24-h period. Pharmacokinetic parameters assessed included area under the concentration-time curve (AUC), maximum concentration (Cmax) of macimorelin in plasma, time to Cmax (tmax), and terminal elimination half-life (t1/2). Pharmacodynamic assessments evaluated levels of GH, adrenocorticotropic hormone, thyroid-stimulating hormone, cortisol, and prolactin. Safety was assessed based on treatment-emergent adverse events (TEAEs), vital signs, 12‑lead electrocardiograms, and laboratory parameters. Results A total of 28 healthy adults were enrolled and completed the study. Macimorelin AUC and Cmax showed less than dose-proportional increases following administration of 0.5 and 1.0 mg/kg. Mean t1/2 was 3.51 h for macimorelin 0.5 and 1.0 mg/kg and 8.29 h for macimorelin 2.0 mg/kg; median tmax occurred at 0.5 to 0.75 h. GH levels increased after dosing, with a tmax of 0.75 h to 1.0 h. Mean GH Cmax was similar with the macimorelin 0.5- and 1.0-mg/kg doses (31.9 and 37.8 ng/mL, respectively) and was ~50% lower with macimorelin 2.0 mg/kg (18.4 ng/mL). Transient increases were observed in adrenocorticotropic hormone, cortisol, and prolactin, which were not dose related. A total of 19 TEAEs were reported in 35.7% (10/28) of participants; all TEAEs were mild or moderate and resolved. A total of 12 drug-related TEAEs were reported in 8 participants. Headache was the most common drug-related TEAE. All doses of macimorelin prolonged mean QTcF by 10 to 11 ms. There were no clinically meaningful changes in vital signs or laboratory parameters. Conclusions Single-dose administration of macimorelin 0.5 to 2.0 mg/kg was well tolerated. Macimorelin exposure was less than dose-proportional over the dose range studied. Administration of macimorelin stimulated GH production, with the greatest increases observed in the macimorelin 0.5- and 1.0-mg/kg groups.