High bioavailability, short half-life, and metabolism into hydromorphone-3-glucuronide following single intramuscular and intravenous administration of hydromorphone hydrochloride to great horned owls (Bubo virginianus)

OBJECTIVE To determine the pharmacokinetic parameters of hydromorphone hydrochloride and its metabolite, hydromorphone-3-glucuronide (H3G), after a single IV and IM dose in great horned owls (Bubo virginianus). ANIMALS 6 healthy adult great horned owls (3 females and 3 males). PROCEDURES A single dose of hydromorphone (0.6 mg/kg) was administered once IM (pectoral muscles) and IV (left jugular) with a 6-week washout period between experiments. Blood samples were collected at 5 minutes and 0.5, 1.5, 2, 3, 6, 9, and 12 hours after drug administration. Plasma hydromorphone and H3G concentrations were determined with liquid chromatography–tandem mass spectrometry, and a noncompartmental analysis was used for the determination of pharmacokinetic parameters. RESULTS Hydromorphone had a high bioavailability of 170.8 ± 37.6% and rapid elimination after IM administration and rapid plasma clearance and a large volume of distribution after IV administration. Mean C_max was 225.46 ± 0.2 ng/mL at 13 minutes after IM injection. Mean volume of distribution and plasma drug clearance was 4.29 ± 0.5 L/kg and 62.11 ± 14.6 mL/min/kg, respectively, after IV administration. Mean t_1/2 was 1.62 ± 0.36 and 1.35 ± 0.59 hours after IM and IV administration, respectively. The metabolite H3G was readily measured shortly after administration by both routes. CLINICAL RELEVANCE A single dose of 0.6 mg/kg was well tolerated in all birds. Hydromorphone rapidly attained plasma concentrations following IM administration and had high bioavailability and short t_1/2. This study is the first to document the presence of the metabolite H3G in avian species, which suggests similar hydromorphone metabolism as in mammals.