| Summary: | Opioid drugs are used to manage moderate to severe pain in mammals and avian species. In dosing opioids for a particular species, it is optimal to use dosing regimens based on pharmacokinetics or pharmacodynamics studies conducted in the same species as variability in the physiology among different species may result in differences in drug pharmacokinetics and pharmacodynamics. Unfortunately, dosing regimens are typically extrapolated from closely related avian species or even mammals, which is unideal. Therefore, this critical review aims to collate and evaluate the dosing regimens of selected opioids: tramadol, hydromorphone, buprenorphine, butorphanol, and fentanyl, in avian species and its related safety, efficacy and pharmacokinetic data. Our review found specific dosing regimens not described in the Exotic Animal Formulary for tramadol used in Indian Peafowl (<i>Pavo cristatus</i>), Muscovy Duck (<i>Cairina moschata</i>) and Hispaniolan Parrot (<i>Amazona ventralis</i>); hydromorphone used in Orange-winged Parrot (<i>Amazona amazonica</i>); buprenorphine used in Cockatiel (<i>Nymphicus hollandicus</i>), American Kestrel (<i>Falco sparverius</i>) and Grey Parrot (<i>Psittacus erithacus</i>); and butorphanol used in Hispaniolan Parrot (<i>Amazona ventralis</i>), Broiler Chicken and Indian Peafowl (<i>Pavo cristatus</i>). Cockatiel appeared to not experience analgesic effects for hydromorphone and buprenorphine, and American Kestrel exhibited sex-dependent responses to opioids. The selected opioids were observed to be generally safe, with adverse effects being dose-dependent.
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