Abstract: Abstract: Objective To measure 95% effective doses (ED95) of propofol and etomidate by using up- down intravenous administration method, and compare the potency ratio and the anesthesia duration of them. Methods Twenty eight male SD rats were divided into two groups randomly: the propofol group and the etomidate group．Loss of righting reflex was regarded as the judgment index of unconsciousness. The dose-response curve was made according to the formula of Y=Ymin + (Ymax-Ymin) / [1 + 10log（ED50- X）× m ]. Values of ED95 of propofol and etomidate were calculated, and the anesthesia duration periods after administration of the two equivalent dose drugs were measured respectively. Results The values of ED95 were 9 mg/kg and 1.5 mg/kg for propofol and etomidate. The ED95 ratio for propofol and etomidate was 6. There was a significant difference in anesthesia duration between propofol group (465.6±18.5)s and etomidate group (233.7±9.3)s (P＜ 0.05). Conclusion The anesthesia duration of propofol is longer than that of etomidate, taking the ED95 as equivalent dose.

Key words:  propofol, etomidate, anesthesia, rats, Sprague- Dawley, up- down method, 95% effective dose, righting reflex