In vivo Dependence Liability Assessment of Novel Fentanyl Analogues: Science to Guide drug Policy

The emergence of fentanyl analogues as drugs of abuse raises concern regarding their dependence liability. Following prolonged opioid administration, physical dependence leads to increased use, which facilitates the development of tolerance and the dangers of overdose. In animal models, opioid dependence can be inferred by assessing signs of withdrawal, with vertical jumping being the most sensitive and easily quantified in the mouse. In this study, we aimed to characterize the dependence liability of fentanyl, morphine, and six fentanyl analogues by assessing antinociception and withdrawal signs elicited by each compound in the mouse. First, to determine antinociceptive effects, we used a warm‐water tail withdrawal procedure using both 50°C and 55°C water. Latencies until mice removed their tails from the water were recorded, and fully effective doses were determined using a 10 second cut‐off to prevent tissue damage. Dose effect‐curves were generated to determine the potency (ED 50 ) of each compound for eliciting antinociception. All analogues were less potent than fentanyl but more potent than morphine. Additionally, all test compounds were fully effective in both 50°C and 55°C water. Next, to assess withdrawal, we treated animals with 3 injections of morphine, fentanyl or the various fentanyl analogues spaced 12 hours apart. Following the first two injections on day 1, we precipitated withdrawal on day 2, 3 hours after the final injection of agonist, using the nonselective opioid antagonist naloxone. Withdrawal sessions lasted 20 minutes and the number of vertical jumps were recorded for each session. Antagonist dose‐effect curves for withdrawal jumps were generated first using an agonist dose one‐log unit higher than the fully effective antinociceptive dose and precipitating withdrawal with 3, 10, and 30 mg/kg of naloxone. Next, we used 30 mg/kg of naloxone to precipitate withdrawal using increasing unit doses of each test compoewund since maximal jumping was elicited using 30 mg/kg of naloxone. Agonist dose‐effect curves were generated starting with the lowest fully effective antinociceptive dose and increasing in half‐log units. Our results indicate that all of these fentanyl derivatives are capable of eliciting dependence and offer valuable insight into their abuse potential. Support or Funding Information These studies supported in part by DEA/NCTR (224‐16‐0505R),) and the University of Arkansas for Medical ScienVA (D‐15‐OD‐002ces This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .