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Effect of Intravenous Clonidine on the Dose of Thiopental Required to Induce Anesthesia

Department of Anaesthesia, St. Vincent's Hospital, Melbourne, Victoria, Australia

Abstract

A randomized, double-blind, controlled trial was conducted to investigate the influence of intravenous clonidine on thiopental dose requirements when used for induction of anesthesia and associated hemodynamic effects. Sixty ASA physical status I or II patients were randomly allocated to one of three treatment groups: normal saline solution (control, n = 20); clonidine (2.5 Mg/kg, n = 20); or clonidine (5 Mg/kg, n = 20). The test drug was administered 15 min before induction of anesthesia with intravenous thiopental. The dose of thiopental to produce loss of lash reflex was recorded as well as mean arterial blood pressure and heart rate at 3-min intervals up to induction of anesthesia and then at 1-min intervals for 5 min. Significant decreases in thiopental dose were observed in both groups receiving clonidine compared with the control group, but there was no significant difference between clonidine groups. With dosage calculated according to total body mass, the control group required 5.50 ± 1.15 mg/kg (mean ± SD) of thiopental, whereas those who received 2.5 Mg/kg of clonidine required 4.15 ± 1.46 mg/kg of thiopental (a reduction of 25%), and those who received 5.0 Mg/kg of clonidine required 3.48 ± 1.06 mg/kg of thiopental (a reduction of 37%). When thiopental dose was adjusted for lean body mass, similar reductions were obtained. Clonidine, in both doses, produced more sedation than control, and the 2.5-mg/kg dose produced less sedation than the larger dose. Mean arterial blood pressure was lower in the groups receiving clonidine. There were no significant differences in heart rate among the three groups. If intravenous clonidine is to be used as an adjunct to general anesthesia, appropriate adjustments to the dosage of intravenous thiopental will be required.