A comparison of two subarachnoid 2-agonists, xylazine and clonidine, with respect to duration of antinociception, and hemodynamic effects in goats

Subarachnoid administration of clonidine and xylazine produces antinociception in several species and in humans. The present study compares these two drugs administered by the subarachnoid route to goats. Goats (n = 6) were randomly assigned to three treatment groups. All animals of each group received 0.06 mg kg−1 clonidine (CLO), 0.1 mg kg−1 xylazine (XIL) and 0.9% saline solution (SS), with aminimum interval of 1 week between treatments. All injections were made into the subarachnoid space between the last lumbar vertebra and the first sacral vertebra. Analgesia, ataxia, sedation, cardiovascular and respiratory effects, and rectal temperature were evaluated at predefined regular time intervals before drug administration (baseline) and after administration. The onset of analgesia by clonidine and xylazinewas observed in 6.8±1.8 and 9.5±2.6min (mean ±S.D.), respectively. Both 2-agonists produced analgesia of dorsocaudal rib areas, flanks, hind limbs, perineum and tail, sedation and ataxia. The duration of antinociception after clonidine administration was 118.8±24 min and after xylazine 88.3±15 min (mean±S.D.). Clonidine and xylazine subarachnoidally administered induced a significant (P < 0.05) decrease in heart and respiratory rates and hypothermia in relation to the basal value. Neither drug significantly altered blood pressure. Both 2-agonist drugs induced frequent diuresis and an increase in salivation. We conclude that subarachnoid clonidine produces longer antinociception with less ataxia than xylazine in goats. However, the drug induced bradycardia, a decrease in the respiratory rate and hypothermia, with a small compromise in the blood pressures at the doses studied. Further studies should be done to determine whether this analgesia is sufficient for surgical procedures. © 2002 Elsevier Science B.V. All rights reserved.