|Pronunciation||bue tor’ fa nol|
|Trade names||Stadol, others|
|Other names||BC 2627|
|Drug class||Opioid agonist–antagonist|
|Main uses||Moderate to severe pain|
|Side effects||Sleepiness, respiratory depression, confusion, feeling high, agitation, itchiness, sweating, nausea, constipation|
|Onset of action||Within 15 min|
|Duration of action||Up to 5 hrs|
|Typical dose||1 to 2 mg|
|Bioavailability||Nasal: 60-70%; Sublingual: 25%-35%; PO 10%|
|Metabolism||Liver hydroxylated & glucuronidated|
|Elimination half-life||4-7 hours|
|Chemical and physical data|
|Molar mass||327.468 g·mol−1|
|3D model (JSmol)|
|(what is this?)|
Butorphanol, sold under the brand name Stadol among others, is an opioid used to treat pain. As a nasal spray, it may be used to treat migraines. By injection into a vein or muscle, it may be used to treat moderate to severe pain. Onset of effects is within 15 minutes and may last up to 5 hours.
Side effects may include sleepiness, respiratory depression, confusion, feeling high, agitation, itchiness, sweating, nausea, and constipation. While there is the potential for misuse, this is less than morphine. Long term use in pregnancy can result in neonatal abstinence syndrome in the baby. It has agonist–antagonist effects at the µ and ĸ type opiate receptors.
Butorphanol was patented in 1971 and approved for medical use in 1978. It is available as a generic medication. In the United States a 1 mg vial for injection costs about 6 USD.  In the United States it is a schedule IV controlled substance.
The most common indication for butorphanol is management of migraine using the intranasal spray formulation. It may also be used parenterally for management of moderate-to-severe pain, as a supplement for balanced general anesthesia, and management of pain during labor. Butorphanol is also quite effective at reducing post-operative shivering (owing to its Kappa agonist activity). Butorphanol is more effective in reducing pain in women than in men.
As with other opioid analgesics, central nervous system effects (such as sedation, confusion, and dizziness) are considerations with butorphanol. Nausea and vomiting are common. Less common are the gastrointestinal effects of other opioids (mostly constipation). Another side effect experienced by people taking the medication is increased perspiration.
Butorphanol exhibits partial agonist and antagonist activity at the μ-opioid receptor, as well as partial agonist activity at the κ-opioid receptor (Ki = 2.5 nM; EC50 = 57 nM; Emax = 57%). Stimulation of these receptors on central nervous system neurons causes an intracellular inhibition of adenylate cyclase, closing of influx membrane calcium channels, and opening of membrane potassium channels. This leads to hyperpolarization of the cell membrane potential and suppression of action potential transmission of ascending pain pathways. Because of its κ-agonist activity, at analgesic doses butorphanol increases pulmonary arterial pressure and cardiac work. Additionally, κ-agonism can cause dysphoria at therapeutic or supertherapeutic doses; this gives butorphanol a lower potential for abuse than other opioid drugs.
Society and culture
Within the INN, USAN, BAN, and AAN naming systems this drug is known as butorphanol, while within JAN it is named torbugesic. As the tartrate salt, butorphanol is known as butorphanol tartrate (USAN, BAN).
Butorphanol is available in the U.S. as a generic drug; it is available in various nations under one of any number of trade names, including Moradol and Beforal (Brand name Stadol no longer available in the US); veterinary trade names include Butorphic, Dolorex, Morphasol, Torbugesic, and Torbutrol.
Butorphanol is listed under the Single Convention on Narcotic Drugs 1961 and in the United States is a Schedule IV Narcotic controlled substance with a DEA ACSCN of 9720; being in Schedule IV it is not subject to annual aggregate manufacturing quotas. The free base conversion ratio of the hydrochloride is 0.69. Butorphanol was originally in Schedule II and at one point it was decontrolled.
In veterinary anesthesia, butorphanol (trade name: Torbugesic) is widely used as a sedative and analgesic in dogs, cats and horses. For sedation, it may be combined with tranquilizers such as alpha-2 agonists (medetomidine), benzodiazepines, or acepromazine in dogs, cats and exotic animals. It is frequently combined with xylazine or detomidine in horses.
Butorphanol is frequently used for post-operative and accident-related pain in small mammals such as dogs, cats, ferrets, coatis, raccoons, mongooses, various marsupials, some rodents and perhaps some larger birds, both in the operating suite and as a regular prescription medication for home use, for management of moderate to severe pain.
Although butorphanol is commonly used for pain relief in reptiles, no studies (as of 2014) have conclusively shown that is an effective analgesic in reptiles.
Butorphanol is a commonly used narcotic for pain relief in horses. It is administered either IM or IV, with its analgesic properties beginning to take effect about 15 minutes after injection and lasting 4 hours. It is also commonly paired with sedatives, such as xylazine and detomidine, to make the horse easier to handle during veterinary procedures.
Side effects specific to horses include sedation, CNS excitement (displayed by head pressing or tossing). Overdosing may result in seizures, falling, salivation, constipation, and muscle twitching. If an overdose occurs, a narcotic antagonist, such as naloxone, may be given. Caution should be used if butorphanol is administered in addition to other narcotics, sedatives, depressants, or antihistamines as it will cause an additive effect.
Butorphanol can cross the placenta, and it will be present in the milk of lactating mares who are given the drug.
The drug is also prohibited for use in competition by most equestrian organizations, including the FEI, which considers it a class A drug.
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