BUTORPHANOL

'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.

Contents

Mechanism of action

Place in therapy

Adverse effects

Proprietary preparations

Use in horses

Side effects, overdose, and precautions

References

Mechanism of action

Butorphanol exhibits partial agonist and antagonist activity at the μ opioid receptor and agonist activity at the κ opioid receptor. The kappa opioid nalbuphine produces gender- and dose-dependent analgesia and antianalgesia in patients with postoperative pain, , RW, Gear, Pain, 1999 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, and narcotic addicts do not like it.

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.
In veterinary use, butorphanol ("Torbugesic") is widely used as a sedative and analgesic in dogs cats and horses. For sedation, it is often combined with medetomidine('Domitor') in dogs, cats and detomidine ('Domosedan' etc) in horses^[1].

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 xylaxine ad 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, consitipation, 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.

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.
1. NOAH Compendium of Data Sheets for Animal Medicines 2005