Oxytocin Pen
10 mg of the cyclic nonapeptide hormone in 3 mL of bacteriostatic water, about 3.33 mg/mL. Filled from a peptide lot tested in the manufacturer’s own laboratory before release. Classified hazardous; see the SDS.
| Compound | Oxytocin (acetate salt as supplied) |
|---|---|
| CAS number | 50-56-6 |
| Molecular formula | C43H66N12O12S2 |
| Contents | Oxytocin: 10 mg per 3 mL pen (0.33% 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
- 10 mg · 1 pen — $98.99
- 10 mg · Kit of 10 — $880.02
Oxytocin is the nine-residue neurohypophysial hormone CYIQNCPLG-NH2, its ring closed by a disulfide between cysteines 1 and 6. This preloaded pen holds 10 mg of oxytocin acetate in 3 mL of bacteriostatic water, about 3.33 mg/mL, made up in advance with no powder to dissolve. Research on the peptide covers the oxytocin receptor and its circuits in animal models, and a body of formulation work on how oxytocin degrades in water, which bears directly on a solution product.
What is in the pen
The 3 mL glass cartridge holds a sterile solution of oxytocin, supplied as the acetate salt, at 0.33% w/v: 10 mg per pen according to the safety data sheet. The solvent is bacteriostatic water with 0.9% benzyl alcohol as an antimicrobial preservative, and the SDS lists no buffer or other excipient. The oxytocin ingredient is classified as toxic if swallowed or inhaled, a respiratory and skin sensitiser, and a category 1A reproductive toxicant that may damage fertility or the unborn child; benzyl alcohol adds its own statements for harm if swallowed or inhaled, eye irritation and skin sensitisation.
Store the pen at 2 to 8 °C in its carton, protected from light, capped once opened and locked up. Do not freeze it, and discard a pen whose solution has frozen, discoloured or become cloudy. The freeze-dried oxytocin 2 mg vial is the alternative, and peptide pen vs vial compares the two formats.
What the research covers
Oxytocin has been studied closely in aqueous solution because a heat-stable liquid formulation has long been a goal for the medicine1. Its weak point is the disulfide. Wiśniewski and colleagues incubated oxytocin and a series of labelled and modified analogues at 40 °C and proposed that degradation begins with beta-elimination at the disulfide, giving a persulfide intermediate that passes a sulfur atom to intact oxytocin to form trisulfides and higher polysulfides2. Hawe's group found that loss of intact peptide was slowest at pH 4.5, with tri- and tetrasulfides and disulfide- or dityrosine-linked dimers forming at pH 4.5 and above1.
Formulation can slow this. Avanti and colleagues showed that citrate buffer combined with at least 2 mM calcium, magnesium or zinc chloride improved the stability of oxytocin solutions at pH 4.5 over four weeks of storage, while the same ions in acetate buffer did not3. The pen's solution contains none of these: the safety data sheet lists only oxytocin, benzyl alcohol and water. No cited study tested oxytocin in bacteriostatic water, so its shelf life in the pen is not established, and the SDS conditions are the ones to follow. The receptor and circuit research is in the oxytocin and neuronal circuits guide.
Frequently asked questions
How does the pen differ from the oxytocin 2 mg vial?
The vial holds 2 mg of freeze-dried oxytocin kept frozen. The pen holds 10 mg already dissolved in 3 mL of bacteriostatic water and is kept at 2 to 8 °C. Oxytocin breaks down in water through its disulfide, so the pen is the format where storage conditions matter most.
Why does pH matter for an oxytocin solution?
In accelerated studies oxytocin degraded fastest at pH 9.0 and slowest at pH 4.5, with deamidation dominating in strong acid and sulfur-linked products and dimers forming at higher pH. The safety data sheet does not state the pH of the pen's solution.
Is the pen hazardous to handle?
The safety data sheet classifies oxytocin as toxic if swallowed or inhaled, a respiratory and skin sensitiser, and a reproductive toxicant that may damage fertility or the unborn child, and benzyl alcohol carries its own warnings. Handle the pen with the precautions in the SDS and keep it locked up.
References
- Hawe A, Poole R, Romeijn S, et al. Towards heat-stable oxytocin formulations: analysis of degradation kinetics and identification of degradation products. Pharm Res. 2009;26(7):1679-88. DOI · PubMed
- Wiśniewski K, Finnman J, Flipo M, et al. On the mechanism of degradation of oxytocin and its analogues in aqueous solution. Biopolymers. 2013;100(4):408-21. DOI · PubMed
- Avanti C, Amorij JP, Setyaningsih D, et al. A new strategy to stabilize oxytocin in aqueous solutions: I. The effects of divalent metal ions and citrate buffer. AAPS J. 2011;13(2):284-90. 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.