Ipamorelin in preclinical protocols: dose ranges, routes, and half-life data from the published record.

Ipamorelin research spans four dose contexts, each corresponding to a different research area. The ranges are not interchangeable — dose, route, species, and study duration interact to produce distinct outcome profiles.

GH-release selectivity studies (Raun et al. 1998): Doses of 1–100 µg/kg administered intravenously to rats for acute GH-pulse measurements.^[1] The 100 µg/kg IV dose is the highest in the selectivity series; at this dose, which exceeds the GH-releasing ED₅₀ by more than 200-fold, ACTH and cortisol remained unchanged.^[1]

Bone biology studies: Johansen et al. 1999 used three dose levels subcutaneously for assessment of longitudinal bone growth — the study reports incremental periosteal growth rates from 42 µm/day to 52 µm/day across doses.^[3] Andersen et al. 2001 used 100 µg/kg SC three times daily for three months in 8-month-old adult female rats — the longest and highest-frequency preclinical dosing protocol in the published record — producing four-fold restoration of periosteal bone formation rate in glucocorticoid-exposed animals.^[4]

GI motility studies (Venkova et al. 2009): Doses ranging 0.01–1 mg/kg IV bolus in male rats for postoperative ileus; single-dose at 1 mg/kg produced accelerated bowel movement; repetitive dosing at 0.1 or 1 mg/kg produced cumulative fecal pellet output and food intake increases.^[5] Doses are expressed in mg/kg here (0.01–1 mg/kg = 10–1000 µg/kg), placing GI motility doses above the acute GH-release range.

Phase 2 clinical trial (NCT00672074): IV infusion in post-surgical human patients.^[15] Specific dose levels are not published in summary; the trial documents use in a clinical-investigational setting. No results were published as an NDA submission.

Plasma half-life: approximately 2 hours in rat and pharmacokinetic model data. GH pulse peak at 15–40 minutes post-injection SC. GH returns to baseline within approximately 3 hours.^[2] Each subcutaneous injection produces one clean GH pulse without a persistent plateau — the pulse architecture that underlies the dosing-frequency rationale in research protocols.

Systemic clearance is approximately 5-fold lower than GHRP-6.^[2] This reduced clearance — ipamorelin is metabolically more resistant — produces more predictable exposure per injection. Route comparisons from Johansen et al.: subcutaneous bioavailability is the primary route used in bone and body composition studies; intranasal bioavailability is approximately 20%, significantly lower but measurable; intravenous is used in acute GH-pulse and GI motility studies.^[2] Excretion is predominantly urinary: 60–80% of administered dose is recoverable intact from urine and bile, distinguishing ipamorelin from GHRP-6 (primarily biliary). Free-acid metabolites persist in urine after the parent compound clears — the basis for the WADA detection window established in Semenistaya et al. 2015.^[9]

For Ipamorelin half-life and pharmacokinetics: t₁/₂ ≈ 2 h, T_max SC 15–40 min, GH-return to baseline ~3 h. These are rodent parameters; human pharmacokinetics have not been formally characterized in published literature.

Dosing frequency varies by research objective in the published record. GH-pulse selectivity studies are acute (single IV dose for immediate hormonal panel measurement).^[1] Bone elongation studies use subcutaneous administration without a stated frequency in the Johansen 1999 study — continuous or daily dosing is implied by the three-month treatment window.^[3] The Andersen 2001 bone protection study explicitly uses three-times-daily SC injection for three months, representing the most intensive preclinical frequency protocol in the record.^[4] GI motility studies use either single IV bolus or repetitive IV dosing within a defined post-surgical observation window.^[5]

Preclinical data on fasted-state versus fed-state timing interactions with GH pulse magnitude has not been characterized in the ipamorelin literature specifically, though both fasted and fed timing contexts appear across protocols. Optimal timing for GH-pulse maximization varies by model and co-agent — ghrelin receptor sensitivity is circadian-modulated in rodent models, but ipamorelin's short half-life (~2 h) means pulse shape is determined primarily by receptor occupancy kinetics rather than circadian gating.

How long for Ipamorelin to work in animal models depends on the endpoint: GH pulse onset is 15–30 minutes post-injection;^[2] bowel motility changes appear within hours in surgical models;^[5] bone formation changes are measured over 3-month treatment windows.^[4]

Three routes appear in the published ipamorelin literature:

Intravenous (IV): Acute pharmacology and GI motility studies.^{[1][5][6][15]} Provides the most controlled PK/PD profile for dose-response characterization. The Phase 2 clinical trial used IV infusion.

Subcutaneous (SC): Bone studies and somatotroph plasticity studies.^[3][4][7] Each SC injection produces one discrete GH pulse with peak at 15–40 min and return to baseline at ~3 h.^[2] Subcutaneous is the predominant route in the literature for studies measuring longitudinal physiological effects.

Intranasal: Characterized by Johansen et al. for bioavailability; approximately 20% systemic exposure relative to IV.^[2] The intranasal route is also the context for the WADA anti-doping metabolite detection study by Semenistaya et al.,^[9] which confirmed that nasal administration leaves a urinary metabolite fingerprint distinct from parenteral administration.

Human clinical pharmacokinetics for any of these routes have not been formally published. The Phase 2 trial (NCT00672074) used IV, but no results describing human PK parameters appear in the public record.^[15] All half-life and clearance figures above are rodent data.