PT-141 Pen
3 mL of the cyclic melanocortin peptide in bacteriostatic water at 10 mg/mL, 30 mg per pen. Filled from a peptide lot tested in the manufacturer’s own laboratory, with a certificate.
| Compound | PT-141 Bremelanotide |
|---|---|
| CAS number | 189691-06-3 |
| Molecular formula | C50H68N14O10 |
| Theoretical mass | 1025.2 Da |
| Sequence / structure | Ac-Nle-cyclo[D-H-[D-Phe]-R-W-K]-OH (7 residues; Asp–Lys side-chain lactam; N-acetyl; free C-terminal acid) |
| Contents | PT-141: 30 mg per 3 mL pen (1% w/v) |
| Form | Sterile aqueous solution in bacteriostatic water (0.9% benzyl alcohol), supplied in a 3 mL glass cartridge inside a preloaded autoinjector pen fitted with a needle |
| Storage, sealed | Store at 2–8 °C in the original carton, protected from light |
| Format | Solution in a 3 mL pre-filled pen |
Sizes and lots
- 30 mg · 1 pen — $78.99
- 30 mg · Kit of 10 — $702.22
PT-141, the development code for bremelanotide, is a cyclic heptapeptide analogue of alpha-MSH that activates melanocortin receptors. This preloaded pen carries 3 mL of bremelanotide solution at 10 mg/mL, 30 mg in all, made up in bacteriostatic water. Published research on the compound runs from the design of cyclic alpha-MSH analogues and the mapping of the melanocortin receptors to studies of hypothalamic activation in rats and two phase 3 trials.
What is in the pen
Each pen holds a 3 mL glass cartridge of sterile aqueous solution. The safety data sheet lists bremelanotide at 1% w/v, which is 10 mg/mL and 30 mg per pen, in bacteriostatic water with 0.9% benzyl alcohol as a preservative. The peptide is the same Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH sold in the PT-141 10 mg vial. At a theoretical mass of 1025.2 Da the pen holds about 29 µmol, close to 9.8 mM. The SDS does not classify bremelanotide as hazardous; for benzyl alcohol it lists harm if swallowed or inhaled, serious eye irritation and skin sensitisation.
What the research covers
Bremelanotide belongs to a family of synthetic alpha-MSH analogues built around a lactam bridge. In 1989 Al-Obeidi and colleagues designed cyclic fragments of the hormone with the help of molecular dynamics and found, in lizard skin assays, that analogues bridged between aspartate and lysine side chains were 90 to 100 times as potent as alpha-MSH itself1. Bremelanotide keeps that Asp-to-Lys ring.
Its targets are the melanocortin receptors. There are five, activated by peptides derived from proopiomelanocortin and opposed by the endogenous antagonists agouti and agouti-related protein, which act at three of them2. Cone's review stressed that the receptors are expressed in a limited number of discrete locations, each tied to fairly circumscribed functions: pigmentation, adrenocortical steroid production, energy homeostasis, natriuresis, erectile responses and exocrine gland secretion2. A ligand that reaches several of these receptors can act on several of those systems at once.
None of the cited papers followed bremelanotide in solution over time, so nothing here establishes how long it stays intact in bacteriostatic water; the storage limits on the safety data sheet are the ones to follow. The design history, receptor binding order, phase 3 trials and the developer's earlier intranasal work are set out in the PT-141 and bremelanotide guide.
Frequently asked questions
How does the pen differ from the PT-141 vial?
The vial holds 10 mg of freeze-dried bremelanotide, stored at −20 °C until a laboratory dissolves it. The pen holds 30 mg already in bacteriostatic water at a fixed 10 mg/mL and is kept at 2 to 8 °C. One keeps the peptide dry for longer storage; the other gives a known concentration from the start.
Has bremelanotide been studied in solution over time?
Not in the papers cited on this page. They cover its design, receptors and trials, but none reports how long it stays intact in bacteriostatic water. The cold, dark, unfrozen conditions on the safety data sheet are the limits to keep the pen within.
References
- Al-Obeidi F, Castrucci AM, Hadley ME, et al. Potent and prolonged acting cyclic lactam analogues of alpha-melanotropin: design based on molecular dynamics. J Med Chem. 1989;32(12):2555-61. DOI · PubMed
- Cone RD. Studies on the physiological functions of the melanocortin system. Endocr Rev. 2006;27(7):736-49. DOI · PubMed
For laboratory research use only. Not for human or veterinary consumption. Products have not been evaluated by the U.S. Food and Drug Administration and are not intended to diagnose, treat, cure or prevent any disease.