Pharmacokinetics and pharmacodynamics of intranasal and intramuscular administration of naloxone in working dogs administered fentanyl

Abstract Background Working dogs exposed to narcotics might require reversal in the field. Objective To explore the pharmacokinetic and pharmacodynamic effects of naloxone administered intramuscularly (IM) or intranasally (IN) to reverse fentanyl sedation in working dogs. Animals Ten healthy, working dogs aged 1.7 ± 1 year and weighing 26 ± 3 kg. Methods In this randomized, controlled cross‐over study dogs received either 4 mg of naloxone IN or IM 10 minutes after fentanyl (0.3 mg IV) administration. Sedation was assessed at baseline and 5 minutes after fentanyl administration, then at 5, 10, 15, 20, 25, 30, 60 and 120 minutes after reversal with naloxone. Blood samples for naloxone detection were obtained at 0, 5, 10, 30, 60 and 120 minutes. Pharmacokinetic parameters and sedation scores were compared between IM and IN naloxone groups. Results There was a significant increase in sedation score from baseline (0.25 [−4 to 1] IM; 0 [−2 to 1] IN) after fentanyl administration (11 [5‐12] IM; 9.25 [4‐11] IN), followed by a significant reduction at 5 (0.5 [−0.5 to 1.5] IM; 1.25 [−1.5 to 4.5] IN) through 120 minutes (−0.5 [−2 to 1] IM; 0 [−4.5 to 1] IN) after reversal with naloxone. Route of administration had no significant effect on sedation score. Maximum plasma concentration was significantly lower after IN administration (11.7 [2.8‐18.8] ng/mL IN, 36.7 [22.1‐56.4] ng/mL IM, P < .001) but time to reach maximum plasma concentration was not significantly different from IM administration. Conclusion and Clinical Importance Although IM administration resulted in higher naloxone plasma concentrations compared to IN, reversal of sedation was achieved via both routes after administration of therapeutic doses of fentanyl.