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Medetomidine is a veterinary anesthetic drug with potent sedative effects and emerging illicit drug adulterant.

It is a racemic mixture of two stereoisomers, levomedetomidine and dexmedetomidine, the latter being the isomer with the pharmacologic effect as an alpha 2- adrenergic agonist. Effects can be reversed using atipamezole.

It was developed by Orion Pharma.^[1] It is approved for dogs in the United States, and distributed in the United States by Pfizer Animal Health and by Novartis Animal Health in Canada under the product name Domitor. The free base form of medetomidine is sold for use as an antifouling substance in marine paints.^[2] It is not licensed for humans but starting in 2022 has been detected in the US in samples of illicit drugs and associated with overdoses.

Medetomidine was developed by Orion Pharma and launched in 2007.^[1]

Medetomidine is a racemic mixture of two optical or stereoisomers, levomedetomidine and dexmedetomidine. ^[3] The latter causes the alpha 2- adrenergic agonist effects.^[4] It is often used as the hydrochloride salt, medetomidine hydrochloride, a crystalline white solid that can be administered as an intravenous drug solution with sterile water.^{[citation needed]}

In veterinary anesthesia, medetomidine is used as both a surgical and analgesic in combinations with opioids (butorphanol, buprenorphine etc.) as premedication (before a general anesthetic) in healthy cats and dogs. It is sometimes used in combination with butorphanol and ketamine (given IM) to produce general anaesthesia for short periods in healthy, but fractious felines, that will not allow an intravenous induction agent to be given providing a good degree of muscle relaxation. It has also been used in combination with morphine (or methadone), lidocaine and ketamine in constant rate infusion analgesia in canines. It is often used in so called microdoses for this analgesic effect. It is thought that this family of drugs has a degree of analgesic action, though this is, in comparison to the sedative effect, minor.

It can be given by intramuscular injection (IM), subcutaneous injection (SC) or intravenous injection (IV). When delivered intravenously, a significantly decreased dose is used. Some authors suggest a sublingual route is also effective. It is not recommended for diabetics, it is contraindicated in patients with cardiac disease.

Due to its potent sedative effects it is commonly used in more aggressive animals, where a drug combination with a lesser effect (such as acepromazine plus an opioid, or an opioid plus a benzodiazepine) would not allow the administration of the inductive agent without risk to the veterinarian. As such the use of alpha-two agonists is only recommended in healthy animals.

Following administration, marked peripheral vasoconstriction and bradycardia are noted.^[5] Often the dosage of induction agents (e.g. propofol) may be drastically reduced, as may the volumes of anesthetic gases (i.e. halothane, isoflurane, sevoflurane) used to maintain general anesthesia.

Its effects can be reversed using atipamezole distributed as Antisedan by Pfizer. IV use of atipamezole is not licensed, IM is the preferred route. Yohimbine may also be used in an emergency situation, but is not licensed.

The free base form of medetomidine is sold as Selektope as an antifouling substance in marine paints.^[2] It is mainly effective against barnacles, as shown in vitro with Balanus improvisus.^[6] It has also shown effect on other hard fouling like tube worms. When the barnacle cyprid larva encounters a surface containing medetomidine the molecule interacts with the octopamine receptor in the larva. This causes the settling larva to increase its kicking to more than 100 kicks per minute, which makes becoming sessile nearly impossible.^[7] When the larva swims away from the surface, the effect disappears (reversible effect). The larva regains its pre-exposure function and can settle somewhere else.

Medetomidine has been found as a component in street drug mixtures in the US starting in 2022,^[3] containing synthetic opioids in a similar manner as xylazine-fentanyl, such mixtures have been nicknamed "tranq" (short for tranquilizer). The combination of α2 adrenergic agonists with opioids are believed to greatly increase the sedative effects of each drug, which some drug users may perceive as a better or more potent product. The Center for Forensic Science Research and Education (CFSRE) first identified a synthetic opioid blend containing fentanyl and medetomidine sold in Maryland in July, 2023. Additional detections in late 2023 found similar medetomidine mixtures in Missouri, Colorado, Pennsylvania, California, and Maryland found in both drug material and the blood of patients experiencing overdoses.^{[8][9][10][11]} In January 2024 drug mixtures containing medetomidine were identified in the Canadian city of Toronto, ON. In April, 2024 and May, 2024 medetomidine was found in a mixture containing fentanyl and xyalazine in Philadelphia, PA^[12] and Pittsburgh, PA. Cases of overdose in Chicago from medetomidine/fentanyl mixtures have been reported In May, 2024.^[13]

Medetomidine was found in combination with the mu-opioid antagonist and kappa-opioid agonist Butorphanol and sedative dopamine antagonist tranquilizer Azaperone in the blood of a 49-year old female homicide victim from Colorado that went missing after a bike ride in 2020. Such a mixture wouldn't be used for recreational use and would instead likely produce dysphoria with heavy sedative effects that may render a person immobile or unable to defend themselves.^[14][15][16]

• Harari J (1996). Small Animal Surgery. Williams and Wilkins. ISBN 978-0-683-03910-8.