By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
Brand Name: Stadol, Torbutrol, Torbugesic, Dolores, Butorphic, Dolorex
Available in 1 mg, 5 mg and 10 mg tablets
The opiate class of medication is complicated to describe. There are several types of receptors in the nervous system that respond to opiates. These receptors are designated by different Greek letters (“mu,” “kappa,” and “sigma”). Opiates work by binding and stimulating some receptors (such opiates are said to be agonists of the receptors they stimulate) or they may bind and block receptors (in which case they are antagonizing the receptor). What the effects of a given opiate are (euphoria, cough suppression, pain relief, hallucination, addiction etc.) depend on which receptors are stimulated and which are blocked.
Some opiates only stimulate receptors. These are called pure agonists. Some opiates, like butorphanol, stimulate some receptors and block others. This makes butorphanol what is called an “agonist/antagonist.” Butorphanol stimulates the kappa receptors (pain relief) and the sigma receptors (cough suppression) and antagonizes the mu receptors (pain relief, euphoria, sedation, nausea, respiratory suppression, constipation). What this boils down to, is that butorphanol makes for only mild very short-acting pain relief but good cough suppression and does so without addiction and with minimal sedation. In a surgical or anesthetic setting, butorphanol can be used to reverse the respiratory depression of mu antagonist (such as fentanyl), should that become problematic, without reversing the pain relief. Butorphanol is also used to relieve nausea associated with certain chemotherapy agents (cisplatin in particular).
The chief side effect is sedation. Occasionally, it can cause diarrhea or appetite loss.
Butorphanol is able to slow the heart rate though this is rarely of meaningful significance to normal patients.
Interactions With Other Drugs
Because butorphanol antagonizes the mu receptor, it will fight against opiates that are mu agonists: morphine, oxymorphone, fentanyl, meperidine, etc.
If butorphanol is used with any other drugs that have sedating properties, these sedating properties will be more blatant.
While butorphanol does not normally cause respiratory suppression, it might if used in conjunction with antihistamines or tranquilizers.
Concurrent use with the antibiotic erythromycin may reduce metabolism of butorphanol, leading to a longer or stronger activity of butorphanol and greater potential for side effects. A similar interaction is seen with the airway dilator theophylline.
Concerns And Cautions
There are several circumstances where butorphanol is considered inappropriate. Butorphanol should be used cautiously or not at all in patients with: liver disease, kidney failure, hypothyroidism, hypoadrenocorticism (Addison's disease), head trauma, hydrocephalus, or in very debilitated patients.
Butorphanol will cross the placenta and will be secreted in milk. It should not be used in pregnancy and lactation.
Butorphanol is removed from the body by the liver. If the liver is diseased, abnormal clearance of it may be seen.
Butorphanol should not be used in respiratory conditions where cough suppression is not desired (such as pneumonia).
This medication is on the list of drugs influenced by the P-1 gene mutation that is common in Collies and Collie-type breeds. The P-glycoprotein is involved in keeping certain drugs out of certain body tissues (the central nervous system in particularly). Many Collies have a mutation in the gene making their central nervous system more available to certain drugs than would be the cases in dogs with normal P-glycoprotein. Butorphanol is one of these drugs involved in this scenario, making dogs with this mutation (the MDR1 mutation) sensitive to the sedation side effect of butorphanol. Dose reduction is recommended. Learn more about this mutation and how to test your dog for it.
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