Medetomidine and atipamezole in sheep: disposition and clinical effects

Abstract

Medetomidine is a selective a 2 -agonist which produces effective sedation and analgesia, and is currently licenced for use in dogs and cats. The effects can be reversed by atipamezole, a selective a 2 -antagonist. This agonist-antagonist combination has also been useful in the reversible immobilization of various non-domestic species (Jalanka, 1993).The clinical effects of medetomidine have also been studied in sheep (Mohammad et al.

The impact ofMK‐467 on plasma drug concentrations, sedation and cardiopulmonary changes in sheep treated with intramuscular medetomidine and atipamezole for reversal

“…This is in contrast to a report by Ranheim et al. (), where sheep that received a similar dose ratio of ATI: medetomidine (5:1) became excited and exhibited muscle tremors. This could be due to the later administration of ATI (60 min) in that study, after considerable decay of the effects of medetomidine.…”

“…These findings seemed to directly reflect the DEX plasma concentrations. Our results support the speculation that in sheep, there was no or limited receptor hysteresis and the degree of sedation directly represented (dex)medetomidine concentrations in plasma (Kästner et al., ; Muge, Chambers, & Livingston, ; Ranheim et al., ), at least with the concentrations detected in our study. In some other ruminants, such as cattle and reindeer, plasma medetomidine concentrations appear to correlate less directly with its sedative effects (Ranheim et al., , , ).…”

“…Ranheim et al. () suggested that ATI might have displaced medetomidine from the highly perfused organs such as kidneys, lungs and liver, thus increasing its plasma concentration. The findings in the present study support this displacement hypothesis.…”

Preanesthesia, Anesthesia, Analgesia, and Euthanasia

“…At higher doses, tolazoline can cause hyperesthesia and transient bradycardia, sinus arrest, and hypotension (Riebold, 2007). Re-sedation following atipamazole reversal of medetomidine, presumably due to redistribution or slower elimination from the central nervous system has been reported in dairy calves but not sheep (Ranheim et al, 1998(Ranheim et al, , 2000a. Re-sedation following atipamazole reversal of medetomidine, presumably due to redistribution or slower elimination from the central nervous system has been reported in dairy calves but not sheep (Ranheim et al, 1998(Ranheim et al, , 2000a.…”

Comparison of two pre-anaesthetic medetomidine doses in isoflurane anaesthetized sheep

“…Medetomidine – like other α 2 ‐agonists in sheep – can induce hypoxaemia and pulmonary oedema after intravenous injection at various doses (Celly et al. 1997b; Ranheim et al. 2000; Kästner et al.…”