PT-141 vs Melanotan II
PT-141 (bremelanotide) and Melanotan II (MT-II) are synthetic melanocortin analogs derived from the same parent peptide, α-MSH. Their structural modifications create distinct receptor selectivity profiles: PT-141 favors sexual function through MC4R agonism, while MT-II produces tanning through MC1R activation.
Structural and Mechanistic Differences
Section titled “Structural and Mechanistic Differences”Melanocortin Receptor System
Section titled “Melanocortin Receptor System”Humans have five melanocortin receptors (MC1R-MC5R):
- MC1R: Skin melanocytes — tanning
- MC2R: Adrenal cortex — cortisol (ACTH receptor)
- MC3R: Hypothalamus — energy homeostasis
- MC4R: Hypothalamus — sexual function, appetite
- MC5R: Exocrine glands — sebaceous secretion
PT-141 (Bremelanotide): MC4R-Selective
Section titled “PT-141 (Bremelanotide): MC4R-Selective”PT-141 modifications enhance MC4R selectivity:
- Structure: [Nle4, D-Phe7]-α-MSH → reduced cyclization
- MC4R EC₅₀: ~0.5 nM (high affinity)
- MC1R EC₅₀: ~10 nM (low affinity)
- MC3R EC₅₀: ~2 nM (moderate affinity)
- Selectivity: MC4R >> MC3R > MC1R
PT-141’s MC4R selectivity drives sexual function without significant tanning.
Melanotan II: Non-Selective
Section titled “Melanotan II: Non-Selective”MT-II retains broad melanocortin receptor activity:
- Structure: Cyclized [Nle4, D-Phe7]-α-MSH analog
- MC1R EC₅₀: ~0.5 nM (high affinity)
- MC4R EC₅₀: ~0.5 nM (high affinity)
- MC3R EC₅₀: ~1 nM (high affinity)
- MC5R EC₅₀: ~2 nM (moderate affinity)
- Selectivity: Non-selective across MC1R-MC5R
MT-II’s non-selectivity produces both tanning and sexual effects, but with more side effects.
| Property | PT-141 | Melanotan II |
|---|---|---|
| Primary target | MC4R | MC1R + MC4R |
| Tanning effect | Minimal | Strong |
| Sexual effect | Strong | Moderate |
| Nausea | 40% | 50-60% |
| Flushing | 20% | 30-40% |
| Priapism risk | Rare | 1-3% (males) |
Tanning vs Sexual Function
Section titled “Tanning vs Sexual Function”PT-141: Sexual Function Focus
Section titled “PT-141: Sexual Function Focus”- FDA-approved: Vyleesi (2019) for premenopausal HSDD
- Mechanism: MC4R activation → hypothalamic dopamine release
- Sexual effects: Increased desire, arousal, orgasm intensity
- Tanning: Minimal due to low MC1R affinity
- Melasma risk: Low (5-10% mild hyperpigmentation)
Melanotan II: Tanning Focus
Section titled “Melanotan II: Tanning Focus”- FDA status: Not approved (research chemical)
- Mechanism: MC1R activation → melanogenesis
- Tanning effects: Deep pigmentation in 5-10 days
- Sexual effects: Present but secondary
- Melasma risk: 20-30% (face, hands)
Clinical Applications
Section titled “Clinical Applications”| Application | PT-141 | Melanotan II |
|---|---|---|
| Female HSDD | FDA-approved | Investigational |
| Male ED | Investigational | Investigational |
| Tanning | Not indicated | Primary use |
| Photoprotection | Not indicated | Investigational |
| Melanoma risk | Not assessed | Concerning |
Half-Life and Pharmacokinetics
Section titled “Half-Life and Pharmacokinetics”PT-141 Pharmacokinetics
Section titled “PT-141 Pharmacokinetics”- Half-life: 2.7 hours (IV), 2.8 hours (SC)
- Bioavailability: 100% (SC)
- Peak concentration: 30-60 minutes
- Duration of effect: 24-48 hours
- Dosing: 1.75 mg SC, PRN (max 8x/month)
Melanotan II Pharmacokinetics
Section titled “Melanotan II Pharmacokinetics”- Half-life: ~1 hour (IV)
- Bioavailability: ~50% (SC)
- Peak concentration: 15-30 minutes
- Duration of tanning: 2-4 weeks
- Dosing: 0.5-1 mg SC daily (tanning protocol)
| Parameter | PT-141 | Melanotan II |
|---|---|---|
| Half-life | 2.7 hours | ~1 hour |
| SC bioavailability | 100% | ~50% |
| Peak (SC) | 30-60 min | 15-30 min |
| Effect duration | 24-48 hours | 2-4 weeks |
| Dosing frequency | PRN | Daily |
Side Effect Profiles
Section titled “Side Effect Profiles”PT-141 Side Effects
Section titled “PT-141 Side Effects”| Side Effect | Incidence | Mechanism |
|---|---|---|
| Nausea | 40% | Central MC4R activation |
| Flushing | 20% | Hypothalamic effects |
| Headache | 15% | Central mechanism |
| Hyperpigmentation | 5-10% | MC1R (minimal) |
| Vomiting | 10% | Central mechanism |
| Injection site reactions | 5% | Local irritation |
| Blood pressure increase | 10-20% | Sympathetic activation |
Melanotan II Side Effects
Section titled “Melanotan II Side Effects”| Side Effect | Incidence | Mechanism |
|---|---|---|
| Nausea | 50-60% | Central MC3R/MC4R activation |
| Flushing | 30-40% | Vasodilation (MC1R) |
| Hyperpigmentation | 80-90% | MC1R-mediated melanogenesis |
| Loss of appetite | 30% | MC4R-mediated anorexia |
| Priapism | 1-3% (males) | MC4R-mediated erection |
| Fatigue | 20% | Central mechanism |
| Facial moles darkening | 40% | MC1R activation |
Nausea Comparison
Section titled “Nausea Comparison”Both agents produce significant nausea through central melanocortin receptor activation. PT-141’s nausea (40%) is slightly lower than MT-II’s (50-60%) due to MC4R selectivity. MT-II’s broader receptor profile activates more emetic pathways.
Administration Routes
Section titled “Administration Routes”PT-141
Section titled “PT-141”- Route: Subcutaneous injection
- Device: Prefilled autoinjector (Vyleesi)
- Dose: 1.75 mg per injection
- Timing: 45 minutes before sexual activity
- Storage: Room temperature
Melanotan II
Section titled “Melanotan II”- Route: Subcutaneous injection
- Device: Lyophilized powder, reconstituted
- Dose: 0.5-1 mg per injection
- Timing: Daily during tanning protocol
- Storage: Refrigerated after reconstitution
References
Section titled “References”- Clayton AH, et al. “Bremelanotide for hypoactive sexual desire disorder in premenopausal women.” J Clin Psychiatry 2017;78:1156-1163.
- Hadley ME, et al. “Discovery and development of melanocortin agonists.” Peptides 2000;21:1587-1599.
- Dorr RT, et al. “Tanning agent Melanotan II: pharmacology and clinical trials.” Cancer Chemother Pharmacol 1996;37:129-135.
- Wikberg JES, et al. “Melanocortin receptors and their ligands.” Pharmacol Res 2000;42:285-294.
- Goldstein I, et al. “Bremelanotide: new treatment for hypoactive sexual desire disorder.” Drugs 2019;79:501-512.