Etorphine

Overview
Etorphine (Immobilon® or M99) is a semi-synthetic opioid possessing an analgesic potency approximately 1000-3000 times that of morphine depending on the test. 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. 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.

A close relative, dihydroetorphine has been used as opiate painkiller for human usage in China. It is claimed to be less addictive than traditional opioids but this has yet to be confirmed.

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

Legal status
In Hong Kong, Etorphine is regulated under Schedule 1 of Hong Kong's Chapter 134 Dangerous Drugs Ordinance. It can only be used legally by health professionals and for university research purporses. The substance can be given by pharmacists under a prescription. Anyone who supplies the substance without prescription can be fined $10000(HKD). The penalty for trafficking or manufacturing the substance is a $5,000,000 (Hong Kong dollar) fine and life imprisonment. Possession of the substance for consumption without license from the Department of Health is illegal with a $1,000,000 (HKD) fine and/or 7 years of jail time.

In the Netherlands, Etorphine is a list I drug of the Opium Law. It is only used for veterinary purposes in zoo's to inmobilise large animals.

In the US, Etorphine is listed as a Schedule I drug, although Etorphine hydrochloride is classified as Schedule II.

In popular culture
Etorphine is the drug which the main character in the books and TV-series about the serial killer and blood spatter specialist Dexter uses to immobilize his victims. In one episode of the TV-series it is shown that the character uses a fake doctor's name to obtain the controlled substance.