Butorphanol (injection)

Butorphanol (injection)

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Clinical data
Pregnancy category	C/D (U.S.)
Routes of administration	IV, intranasal
ATC code	N02AX02 (WHO)
Legal status
Legal status	US: Schedule IV
Pharmacokinetic data
Bioavailability	Nasal: 60-70%
Metabolism	Hepatic hydroxylated & glucuronidated
Elimination half-life	4-7 hours
Excretion	Renal, 75% Biliary, 11-14% Fecal, 15%
Identifiers
IUPAC name 17-cyclobutylmethyl- morphinan-3,14-diol
CAS Number	42408-82-2
PubChem CID	5361092
DrugBank	APRD00835
E number	{{#property:P628}}
ECHA InfoCard	{{#property:P2566}}
Chemical and physical data
Formula	C21H29NO2
Molar mass	327.473

Overview

Butorphanol (INN) is a morphinan-type synthetic opioid analgesic marketed in the U.S. under the trade name Stadol. It is most closely structurally related to dextromethorphan. Butorphanol is available only as butorphanol tartrate in injectable and intranasal spray formulations.

Mechanism of action

Butorphanol exhibits partial agonist and antagonist activity at the μ opioid receptor and agonist activity at the κ opioid receptor. 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.

Place in therapy

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 more effective in reducing pain in women than in men.

Adverse effects

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).

Proprietary preparations

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, Beforal, Stadol, and Stadol NS; veterinary trade names include Butorphic, Dolorex, Morphasol, Torbugesic, and Torbutrol.

Use in horses

Butorphanol is a commonly used narcotic for pain relief in horses. It is administered either IM or IV, with its analgestic 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 proceedures.

Side effects, overdose, and precautions

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.

References

• Katzung, Bertam G. (Ed.) (2001) Basic & Clinical Pharmacology (8th ed.). New York: McGraw-Hill. ISBN 0-8385-0598-8.
• DiPiro, Joseph T. et al. (2005) Pharmacotherapy: A Pathophysiologic Approach (6th ed.). New York: McGraw-Hill. ISBN 0-07-141613-7.
• Stadol NS - monograph
• Forney, Barbara C, MS, VMD. Equine Medications, Revised Edition.' Blood Horse Publications. Lexington, KY. Copyright 2007.
• The Merck Manual of Vetrinary Medicine, 2004 edition (English)
• The Merck Manual, 2004 Edition (German)
• Mosby's Drug Guide 2004
• Various Usenet (alt.drugs.hard, alt.drugs.valium and rec.pets.cats) discussions about surgery on cats and a cat who was injured by being hit by am automobile.
• Surgery-related episode from c.a. June 2004 of "The Crocodile Hunter" television programme, section on doing surgery on a crocodile and shortly thereafter a Fierce Snake -- specifically commentary by Steve Irwin on the dangers that most or all general anaesthetics pose to reptiles and amphibians.