[Effects of oral alpha 2 adrenergic agonists, clonidine and tizanidine, on tetracaine spinal anesthesia]

This study was conducted to evaluate the effects of oral clonidine and tizanidine, alpha 2 adrenergic agonists, as premedication for tetracaine spinal anesthesia in 63 gynecological patients. The patients were randomly allocated to one of six groups. Group 1 (n = 7), group 2 (n = 8) and group 3 (n = 7) received 13 mg of tetracaine intrathecally in 10 % glucose solution 2.6 ml. Group 4 (n = 13), group 5 (n = 14) and group 6 (n = 13) received 13 mg of tetracaine intrathecally in a volume of 2.6 ml of 10 % glucose solution which contained 0.65 mg of phenylephrine. As premedication, group 1 and 4 received 0.25 mg of oral triazolam; group 2 and 5 received 3 mg of oral tizanidine; group 3 and 6 received 0.15 mg of oral clonidine. Group 2 and 3, or group 5 and 6 (clonidine or tizanidine group, respectively) needed significant longer time for regression of Th10 sensory blockade than group 1 or 4 (triazolam). The time for appearance of postoperative pain and the time to require postoperative analgesics were longer in the groups which had received either clonidine or tizanidine than in the groups which had received triazolam. Heart rate and systolic blood pressure in group 6 (clonidine-tetracaine-phenylephrine group) showed significant decreases (P0.05) after the spinal anesthesia. We concluded that oral premedication of clonidine and tizanidine prolonged tetracaine spinal anesthesia. From the view point of the prolongation of spinal anesthesia and the hemodynamic stability, oral premedication with tizanidine seems to be useful.