Pharmacokinetics of Intravenous and Intramuscular Nalbuphine in Isoflurane‐Anesthetized Chickens ( Gallus gallus domesticus )

This study aimed to determine the pharmacokinetics of nalbuphine following intravenous (IV) or intramuscular (IM) administration in six adult H&N Brown chickens anesthetized with isoflurane. In a randomized crossover study, nalbuphine (12.5 mg/kg) was administered IV and IM to isoflurane-anesthetized chickens (end-tidal isoflurane concentration: 1.2%-1.4%), with 1-week intervals between experiments. Blood samples were collected immediately before and at predetermined time points up to 480 min after administration. Plasma concentrations were determined by liquid chromatography-mass spectrometry, and models were fitted to plasma concentration versus time data. Cardiovascular variables were recorded concurrently at the same time points. A three-compartment model best described nalbuphine plasma concentration changes. Estimated distribution volumes were 1.4 L/kg for the central compartment and 0.57 and 2.5 L/kg for the first and second peripheral compartments, respectively. Metabolic clearance was 7.59 L/kg/h, and distribution clearances were 0.25 and 11 L/kg/h for the first and second peripheral compartments, respectively. Bioavailability after IM administration was 98%. The plasma concentration at time zero was 11.81 mg/L. Heart rate slightly decreased at 4 and 8 min after IV or IM drug administration. Nalbuphine exhibited a high volume of distribution and clearance in isoflurane-anesthetized chickens, and demonstrated excellent bioavailability after IM administration.