Macimorelin
Macimorelin. An orally active peptidomimetic agonist at the growth hormone secretagogue receptor, used diagnostically rather than… Oral half-life 4.1 h.
An orally active peptidomimetic agonist at the growth hormone secretagogue receptor, used diagnostically rather than therapeutically: a single oral dose provokes a growth-hormone peak and a subnormal peak diagnoses adult growth hormone deficiency. Macrilen label section 12.1 verbatim: "Macimorelin stimulates GH release by activating growth hormone secretagogue receptors present in the pituitary and hypothalamus", and section 12.2: "Maximum GH levels are observed between 30 to 90 minutes after administration of MACRILEN." NOTE THE PD AND PK ARE DIFFERENT ANALYTES ON DIFFERENT CLOCKS — growth hormone peaks at 30-90 min while macimorelin itself peaks at 0.5-1.5 h. NO RECEPTOR AFFINITY IS AUTHORED: the discovery paper has macimorelin as its subject and measured binding to human pituitary GHS receptors and hGHS-R1a, but prints no constant, calling it only "high potency" (PMID:12646029); its full text was NOT RETRIEVED, being outside the PMC open-access subset.
PubChem free base CID 9804938 (C26H30N6O3, 474.6) and acetate CID 71526737 (C28H34N6O5, 534.6), both re-queried 2026-09-26; the label's own section 11 mass for the acetate agrees exactly. THE STORED DOSE IS A DECLARED CONVERSION, not a figure the label prints: the label says "The recommended dose is a single oral dose of 0.5 mg/kg of macimorelin", and 0.5 mg/kg at this catalog's 70 kg reference is 35 mg, which is what is stored so that a fixed-mg consumer sees the right exposure. A GROWTH-HORMONE TRAP THAT MUST NOT BECOME A MACIMORELIN Cmax: PMID:32325373 reports "Mean GH Cmax was similar with the macimorelin 0.5- and 1.0-mg/kg doses (31.9 and 37.8 ng/mL, respectively)" — those ng/mL are GROWTH HORMONE, the pharmacodynamic readout, and the units make them look plausible as the drug's own concentration. Macimorelin's real parent-drug Cmax values are 3.46, 8.13 and 12.87 ng/mL at 0.25, 0.5 and 1.0 mg/kg, and they are in CHILDREN with suspected GHD, not healthy adults (PMID:34438400). PROTEIN BINDING IS NOT STATED anywhere — not in the label, not in either PK paper — so no fraction_unbound is stored. FOOD EFFECT AND METABOLISM, both from the LABEL and neither from any PMID named nearby, so both are described rather than quoted: a liquid meal decreases macimorelin Cmax and AUC by 55% and 49%, and an in vitro human liver microsome study makes CYP3A4 the major metabolising enzyme. A HUMAN IV DOSE EXISTS UNDER A DIFFERENT NAME and is not treated as this record's: PMID:12240910 gives "acute i.v. EP1572 administration (1.0 microg/kg)" in 2 men, never using the word macimorelin, so it is development-code identity in n=2 and yields no PK.
Pharmacokinetics
- Oral — t½ 4.1 h · F 100%
Sources: PMID:32325373, PMID:34438400, PMID:12646029, PMID:12240910