Which opioid has M-5050 as its reversal agent?

• A. Carfentanil
• B. Buprenorphine
• C. Etorphine
• D. Methadone

Answer: (C)

Reversal of ultra-potent veterinary opioids requires a specific antagonist with high affinity for the mu receptor. M-5050 is diprenorphine, the antidote used to reverse etorphine’s effects in wildlife anesthesia. Diprenorphine binds strongly to mu receptors and displaces etorphine, quickly reversing the sedation and respiratory depression caused by etorphine. Etorphine is used for immobilizing large animals precisely because of its extreme potency, so a dedicated antagonist like diprenorphine is essential.

The other opioids listed aren’t reversed by M-5050. Carfentanil, methadone, and buprenorphine require different management; for example, naloxone or naltrexone may be used, but buprenorphine’s high receptor affinity and partial agonist activity can complicate reversal.