Butorphanol and nalbuphine are examples of kappa agonists/mu antagonists and are generally considered opioid agonists-antagonists. They are weaker analgesics in comparison to full agonist opioids.
Butorphanol has veterinary formulations available that originally were labeled for use as an antitussive agent in dogs. It is now approved for veterinary use as an analgesic in cats and horses although its clinical application extends outside these species.13
Butorphanol’s duration of action varies greatly dependent on factors such as species, route of administration, degree of pain experienced by the patient and dosage14, 15, 16, 17. Considering these factors it is assumed the duration of effect is between 1 and 3 hours.18
Within the anesthetic context, butorphanol is routinely used as a premedication because of its sedative and mild analgesic qualities in dogs, cats, horses, ruminants and birds. Routes of administration include intravenous, intramuscular and subcutaneous delivery. Side effects are similar to other opioids, dose dependent respiratory and cardiovascular depression, but are characteristically less than full agonists.
Butorphanol has also been administered as a “partial” reversal agent for full mu agonists. However, conflicting evidence can be found with regard to the reversal capabilities and as to whether or not it can enhance co-administration with a full agonist19, 20. Nalbuphine is similar to butorphanol in pharmacology but used more predominately in humans than veterinary patients; however, nalbuphine is uncontrolled in the USA where butorphanol is a schedule III drug based on human abuse potential.