Macimorelin (Macrilen) is an orally active ghrelin agonist approved by the FDA (December 20, 2017) specifically for diagnosing adult growth hormone deficiency (AGHD).
Mechanism of Action
Stimulates GH secretion from the pituitary by binding to ghrelin receptors (GHSR1a).
Diagnostic Protocol
Administration
- Single oral dose: 0.5 mg/kg
- Taken on empty stomach
Blood Sampling
GH levels measured over 90 minutes:
- Baseline, 30, 45, 60, 90 minutes post-dose
Interpretation
- GH peak ≥2.8 ng/mL: AGHD unlikely
- GH peak <2.8 ng/mL: Suggestive of AGHD
Advantages Over Insulin Tolerance Test (ITT)
| Feature | Macimorelin | ITT |
|---|---|---|
| Route | Oral | IV insulin |
| Hypoglycemia | No | Yes (required) |
| Contraindications | Fewer | Coronary disease, seizures |
| Patient experience | Simple | Unpleasant |
Safety
Well-tolerated with mild, transient side effects:
- Dysgeusia (taste disturbance)
- Dizziness, headache, nausea
Current Status
FDA-approved but commercial sales temporarily discontinued. Manufacturer seeking new partner for re-launch.