Pharmacokinetics of hydromorphone after intravenous and intramuscular administration in male rhesus macaques (Macaca mulatta)

This study reports the pharmacokinetics of hydromorphone after intravenous and intramuscular administration to rhesus macaques (Macaca mulatta). Hydromorphone (0.075 mg/kg) was administered intravenously as a bolus or intramuscularly on separate occasions to healthy, socially housed, socially reared, adult, intact male rhesus macaques (n = 4). Blood samples were collected prior to and until 10 h after administration. Serum hydromorphone concentrations were analyzed with liquid chromatography-mass spectrometry. Compartment models were fit to time-concentration data. A 3-compartment model with input in and elimination from the central compartment best fit intravenous data, whereas a 1-comparment model best fit intramuscular data. After intravenous administration, the median clearance and terminal half-life were 37.7 (range, 33.7 to 47.1) mL/kg/min and 142 (range, 131 to 218) min, respectively. The median (range) elimination half-life after intramuscular administration was 81.5 (77.2 to 92.5) min. Median intramuscular bioavailability was 92% (range, 75% to 104%). Rhesus macaques maintained concentrations greater than or equal to 4.0 ng/mL for at least 2 h after intravenous and intramuscular administration. The disposition of hydromorphone was characterized by a large volume of distribution and moderate clearance. Intramuscular administration resulted in rapid and almost complete drug absorption. Whole-body pruritus, sedation, and decreased appetite were observed in all macaques after initial drug administration.