Diprenorphine

Diprenorphine (Revivon, M5050) is an opiate antagonist used to reverse the effects of the super-potent opioid analgesics such as etorphine and carfentanil that are used for tranquilizing large animals in veterinary medicine.

Diprenorphine is the strongest opiate antagonist that is commercially available (some 100 times more potent as an antagonist than nalorphine), and is used for reversing the effects of very strong opioids for which the binding affinity is so high that naloxone does not effectively or reliably reverse the narcotic effects. These super-potent opioids are not used in humans because the dose for a human is so small that it would be difficult to measure properly, so there is an excessive risk of overdose leading to fatal respiratory depression. However conventional opioid derivatives are not strong enough to rapidly tranquilize large animals such as elephants and rhinos, so drugs such as etorphine or carfentanil are available for this purpose.

Diprenorphine is considered the specific antagonist for etorphine and carfentanil, and is normally used to remobilise animals once veterinary procedures have been completed, however it may also be used on humans in the event that they are accidentally exposed to etorphine or carfentanil, for instance if someone working with large animals suffered a needlestick injury with a dart from a tranquiliser dart gun that was loaded with etorphine or carfentanil, they would be given diprenorphine as an antidote.

In theory diprenorphine could also be used as an antidote for treating overdose of certain opioid derivatives which are used in humans, such as buprenorphine, for which the binding affinity is so high that naloxone does not reliably reverse the narcotic effects. However diprenorphine is not generally available in hospitals, instead a vial of diprenorphine is supplied with the etorphine or carfentanil specifically for reversing the effects of these drugs, so use of diprenorphine for treating buprenorphine overdose is not carried out in practice although it would work in theory.