Administração epidural de neostigmina, epinefrina, xilazina ou associações em éguas: efeitos clínicos e antinoceptivos

Abstract

Failure to administer drugs via the epidural route is a problem more frequently reported in horses than in other species. Studies conducted on humans, mice, goats, and dogs have led to the hypothesis that neostigmine, adrenaline, and their combinations with lidocaine and xylazine may intensify and prolong the antinociceptive effects of the latter two drugs when administered to mares via the epidural route. To test this hypothesis, the current study was divided into four phases, with the same animals being used in all phases. The drugs neostigmine, lidocaine, and their combinations were evaluated in the first phase, and stimulation with a fine needle was used as the nociception model. Because the results differed from those obtained in similar studies, the same drugs were tested in the second phase but by using a different nociception model, i.e., electrostimulation. The results were in line with those obtained in the first phase of this study. The drugs evaluated in the third phase were adrenaline and neostigmine, combined or not with lidocaine, and with electrostimulation as the nociception model. Xylazine, adrenaline, neostigmine, and their combinations were used in the fourth and last phase of this study, and electrostimulation was maintained as the nociception model. Lidocaine was effective in promoting antinociception in the perineal region for a short period, during which the addition of neostigmine did not improve its antinociceptive action in both nociception models (fine needle and electrostimulation). Adrenaline intensified and prolonged the antinociceptive effects of lidocaine, as was observed in studies on humans and other animal species, without triggering any adverse effects. Neostigmine further intensified the antinociceptive effects of the combination of adrenaline and lidocaine. The best results with regard to antinociceptive action were obtained with xylazine; the combination of this drug with neostigmine did not lead to a significant increase in its antinociceptive potency. The small number of animals, use of a single dose of each drug, and use of only two models of nociception were some of the limitations of the present study. Nevertheless, these findings may provide useful information for future research.