Note Pharmacology 1 2 Context - sensitive half - time of fentanyl in dogs 3 4

20 Context-sensitive half-times (CSHTs) of fentanyl in dogs were determined using 21 pharmacokinetic models reported by Murphy et al. and Sano et al., and compared with a 22 human model. The CSHT was defined as the time required for a 50% decrease in drug 23 concentration in the central compartment after the termination of infusion. Although 24 CSHTs increased gradually as the infusion time increased, the CSHTs in dogs were 25 shorter than those in humans. The CSHTs at steady-state were 31.3 and 69.2 min in 26 dogs, and 306.5 min in humans. The CSHTs of fentanyl in dogs are apparently shorter 27 than those in humans; therefore, a continuous infusion of fentanyl may be a rational 28 regimen in dogs, even if duration of infusion is extended. 29 30