title: Efficacy and safety of naltrexone hydrochloride for antagonizing carfentanil citrate immobilization in captive Rocky Mountain elk (Cervus elaphus nelsoni).
abstract: We evaluated efficacy and safety of naltrexone for antagonizing carfentanil immobilization in 12 captive Rocky Mountain elk (Cervus elaphus nelsoni) using a randomized incomplete block experiment. In three replicate trials, elk were hand-injected with 10 micrograms carfentanil citrate/kg body weight intramuscularly. Fifteen min after each elk became recumbent, we administered naltrexone HCl (25% of dose intravenously, 75% subcutaneously) dosed at 0 (control), 25, 50, or 100 mg/mg carfentanil; after an additional 15 min of immobilization, controls received 500 mg naltrexone HCl/mg carfentanil. Elk were immobilized in 34 of 36 attempts; the mean (+/-SE) induction time was 3.1 +/- 0.2 min. Regardless of dose, all elk stood < 9 min after receiving naltrexone; controls remained immobilized until they received antagonist. Mean recovery times did not differ with increasing naltrexone dose (P = 0.31) or among individuals (P = 0.16). None of the elk receiving 100 or 500 mg naltrexone/mg carfentanil renarcotized, but three of eight and seven of nine elk receiving 50 and 25 mg naltrexone/mg carfentanil, respectively, showed signs of mild renarcotization 8 to 24 hr later (P = 0.0002). We observed no adverse clinical effects in elk receiving < or = 500 mg naltrexone/mg carfentanil. Based on these data, we recommend 100 mg/mg carfentanil as a minimum effective dose for rapidly antagonizing immobilization and preventing renarcotization.
authors.affiliation: Colorado Division of Wildlife, Wildlife Research Center, Fort Collins 80526, USA.
authors.forename: M W
authors.initials: MW
authors.lastname: Miller
authors.forename: M A
authors.initials: MA
authors.lastname: Wild
authors.forename: W R
authors.initials: WR
authors.lastname: Lance
mesh_terms: D000701:Analgesics, Opioid / Q000037:antagonists & inhibitors*; D000818:Animals; D003670:Deer / Q000502:physiology*; D005260:Female; D005283:Fentanyl / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors; D007103:Immobilization; D008297:Male; D009271:Naltrexone / Q000009:adverse effects / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000009:adverse effects / Q000494:pharmacology*
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009271:Naltrexone; C017114:carfentanil; D005283:Fentanyl