Etorphine (Immobilon® or M99) is a synthetic cousin of morphine and 1000 - 80,000 times more powerful. It was invented in 1963 by a research group at McFarlan-Smith and Co. in Edinburgh, led by Professor Kenneth Bentley. It can be produced from thebaine. It is most often used to immobilize elephants and other large mammals. Etorphine is only available legally for veterinary use and is strictly governed by law. Its chemical name is 6,14-endoetheno–7a(1-(R)-hydroxy-1-methylbutyl)-tetrahydro-nororipavine hydrochloride; its CAS number is 14521-96-1. Diprenorphine (M5050) is an opioid receptor antagonist that can be administered in proportion to the amount of etorphine used (1.3 times) to reverse its effects.

Large Animal Immobilon is a combination of etorphine plus acepromazine maleate. An etorphine antidote Large Animal Revivon contains mainly diprenorphine for animals and a human-specific naloxone-based antidote, which should be prepared prior to the etorphine.

Pharmacology

---

Etorphine is an agonist at $\backslash mu$, $\backslash delta$, and $\backslash kappa$ opioid receptors. It also has a weak affinity for the ORL1 nociceptin/orphanin FQ receptor.

Reference

---

• Bentley KW, Hardy DG. Proc Chem Soc 1963;220.; J.Amer.Chem.Soc., 1967, 89, 3281-3292

External links

---

• Opioids.com page on etorphine
• Etorphine: Molecule of the Month
• Action at Nociceptin Receptor

Semisynthetic opioids | Mu-opioid agonists

Etorphin | Etorfin