The Anesthetic Effect of Dexmedetomidine Does Not Adhere to the Meyer-Overton Rule but Is Reversed by Hydrostatic Pressure

Abstract

To test the hypothesis that the anesthetic action of dexmedetomidine is similar to that of other anesthetics, dexmedetomidine was studied using two classical descriptors of anesthesia, the Meyer-Overton correlation and the pressure reversal of anesthesia. The anesthetic potency of dexmedetomidine and its isomer, levomedetomidine, were determined in Xenopus laevis tadpoles. Anesthesia was defined as loss of righting reflex. Octanol/water partition coefficients were determined using ultraviolet absorbance spectrophotometry. Pressure experiments were performed at pressures ranging from 1 to 91 atmospheres absolute (ata). A concentration-response curve was obtained with a half-maximum effective concentration (EC50) of dexmedetomidine of 7.1 +/- 1.1 micro M (mean +/- SEM), whereas levomedetomidine showed an EC50 of 59.3 +/- 5.5 micro M. The octanol/water partition coefficient was 206 +/- 49. With increasing pressure, the EC50 of dexmedetomidine increased linearly up to a value of 23.9 +/- 3.2 micro M at 91 ata. Correlation of lipid solubility and anesthetic potency demonstrates that dexmedetomidine does not adhere to the Meyer-Overton rule. However, the anesthetic action of dexmedetomidine is diminished by increased pressures, thus demonstrating a similar effect compared with other general anesthetics. (Anesth Analg 1997;84:618-22)