Abstract
Opioids are potent analgesics and are believed to be the best choice for moderate and severe nociceptive pain. Investigating all the possible administration route options for pain management in the different animal species is warranted in horses as systemic administration of these drugs in horses is difficult. In this study the authors describe for the first time in the literature the administration of methadone orally to MDR1 genotipically normal horses. Twelve adult healthy horses (6 females and 6 males) were studied. Horses randomly received one of the doses of methadone (0.1, 0.2, and 0.4mg/kg) per os, which was administered using a 60cc syringe containing 30ml of corn syrup The results showed all doses produced plasma levels compatible to analgesic plasma levels in human beings. The authors conclude that methadone is absorbed when orally administered in horses at doses of 0.1, 0.2, and 0.4 mg.kg -1 . It does not produce excitement, sedation, nor undesirable side effects in healthy horses. Further studies are necessary in order to establish clinical guidelines for oral methadone as an alternative for pain m anagement in the horse.
Highlights
Pain management is advancing continuously in veterinary medicine
Considering the high analgesic efficacy of oral methadone reported in people and the lack of information regarding pharmacokinetics of oral opioids in horses, the purpose of this study was to determine the pharmacokinetic of methadone administered orally to horses
Blood samples were collected through a 14-gauge catheter previously placed on the left jugular vein in order to measure the concentration of methadone in the serum of horses
Summary
Pain management is advancing continuously in veterinary medicine. In equine medicine, it has been shown a relevant clinical importance in shortening and improving recovery of animals in trauma, for surgical patients, and in the postoperative period [1,3,11, 13]. Oral methadone has been widely studied in human medicine as an alternative route to systemic administration of opioids. Methadone is an N-methyl-D-aspartate (NMDA) receptor antagonist and functions as a norepinephrinereuptake inhibitor. These particular characteristics may enhance the analgesic efficacy of methadone when compared to other therapeutic drugs [12]
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