Buprenorphine
Buprenorphine is a highly versatile, widely used **opiate partial agonist** in veterinary medicine. It is primarily utilized for the management of mild to moderate acute pain, particularly in small animals, and is often incorporated into short-term immobilization 'cocktails' alongside alpha-2 agonists and dissociatives. * **Clinical Pearl**: Buprenorphine exhibits a "ceiling effect" at standard doses, meaning that escalating the dose beyond a certain point may not yield additional analgesia and could theoretically decrease analgesic efficacy. * **Feline Advantage**: Cats have a relatively alkaline oral pH, which renders buprenorphine highly lipophilic and allows for excellent **oral transmucosal (OTM) / buccal absorption**. In cats, buccal administration is nearly as bioavailable as an intramuscular injection, making it a highly practical route for at-home post-operative pain management. * **Duration**: It has a longer onset of action compared to pure mu-agonists (like fentanyl or methadone) but provides a significantly longer duration of analgesia (typically 6-8 hours, up to 12 hours). * **Regulatory**: It is a DEA Schedule III controlled substance.
Mechanism: Buprenorphine exerts its analgesic effects by acting as a **partial agonist at the mu (ฮผ) opioid receptor** and an **antagonist at the kappa (ฮบ) opioid receptor** in the central nervous system. * **High Affinity, Slow Dissociation**: It binds to the ฮผ-receptor with an affinity approximately 30 times greater than morphine. This tight binding โ prolonged duration of action. * **Receptor Competition**: Because of its high affinity, it can displace pure ฮผ-agonists from the receptor, potentially antagonizing their analgesic effects while reversing their sedative and respiratory depressant effects. * **Naloxone Resistance**: Its slow dissociation from the receptor makes it notoriously difficult to fully reverse with standard doses of the opioid antagonist **naloxone**; high doses of naloxone or the use of doxapram may be required in cases of severe respiratory depression.
Dosing by species
- Analgesia ยท 0.005-0.02 mg/kg IM, IV or SC q6-12h ยท IM, IV, SC ยท q6-12h
- Analgesia ยท 2-4 micrograms/kg/hour ยท IV ยท continuous infusion
- Analgesia ยท 0.005-0.03 mg/kg IV, IM, SC, epidural ยท IV, IM, SC, epidural
- Analgesia ยท 0.006-0.02 mg/kg IV, IM, SQ ยท IV, IM, SQ ยท 6-12 hours ยท Relatively effective analgesic, but may be difficult to reverse with naloxone if untoward effects are seen.
- Analgesia ยท 0.02 mg/kg ยท IV, IM, SC ยท q6h ยท SC route is listed in historical dosing but text notes it is not recommended due to potentially lower efficacy compared to IM/IV.
- Analgesia ยท 0.01-0.05 mg/kg SC or IM 2-3 times daily ยท SC, IM ยท 2-3 times daily
- Analgesia ยท 0.01-0.03 mg/kg IM, IV, Buccal ยท IM, IV, Buccal ยท up to 6 hours ยท Buccal use is well accepted by cats.
- Analgesia ยท 0.01-0.03 mg/kg PO transmucosally (squirted directly into the mouth) q8h ยท PO transmucosal ยท q8h
- Analgesia ยท 0.01-0.03 mg/kg IM, IV, SC q6-8h; 0.01-0.03 mg/kg PO q6-12h ยท IM, IV, SC, PO ยท q6-12h
- Analgesia ยท 1-3 micrograms/kg/hour ยท IV ยท continuous infusion
Routes of administration
Contraindications
- Known hypersensitivity to buprenorphine
Adverse effects
- Respiratory depression (rare but significant)
- Sedation
- Urine retention or difficulty voiding (particularly with high IV or epidural doses)
- Excitement (horses)
- Diminished gut sounds (horses)
- Vomiting (rare in cats)
Drug interactions
- Local Anesthetics (mepivacaine, bupivacaine) ยท May be potentiated by concomitant use of buprenorphine
- Anticonvulsants (phenobarbital, phenytoin) ยท May decrease plasma buprenorphine levels
- Benzodiazepines ยท Case reports of humans developing respiratory/cardiovascular/CNS depression; use with caution
- CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, alcohol) ยท May cause increased CNS or respiratory depression when used with buprenorphine
- Erythromycin ยท Can increase plasma buprenorphine levels
- Fentanyl (and other pure opiate agonists) ยท Buprenorphine may potentially antagonize some analgesic effects, but may also reverse some sedative and respiratory depressant effects
- Halothane ยท Potentially can increase buprenorphine effects
- Azole Antifungals (ketoconazole, itraconazole, fluconazole) ยท Can increase plasma buprenorphine levels
- Monoamine Oxidase Inhibitors (selegiline, amitraz) ยท Possible additive effects or increased CNS depression
- Naloxone ยท May reduce analgesia associated with high dose buprenorphine
- Pancuronium ยท If used with buprenorphine may cause increased conjunctival changes
- Rifampin ยท Potentially decrease plasma buprenorphine concentrations
Monitoring
- Analgesic efficacy
- Respiratory status
- Cardiac status
Overdose
Buprenorphine has a very high index of safety (ratio of lethal dose to effective dose is at least 1000:1 in rodents). Life-threatening acute overdoses are rare in veterinary medicine, but clinical signs are common. * **Clinical Signs (Dogs)**: Vocalization, ataxia, hypersalivation, hypothermia, and lethargy. * **Treatment**: Supportive care. In cases of acute overdose causing severe respiratory or cardiac effects, **naloxone** and **doxapram** are suggested. > **Note**: Due to buprenorphine's extremely high affinity for the mu-receptor, standard doses of naloxone may be ineffective; very high doses of naloxone may be required to reverse respiratory depression.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.