Comparison of physical dependence of ohmefentanyl stereoisomers in mice

Stereo-structural difference of ohmefentanyl stereoisomers on analgesic action and receptor affinity has been studied. To assess the difference of ohmefentanyl stereoisomers in physical dependence, the potency of physical dependence was quantified by estimating the ED50 value of ohmefentanyl stereoisomers in the naloxone-precipitated jumping test in mice. Morphine was used to assess the method and as a drug of comparison. The results indicate that the degree of physical dependence of morphine can been quantified by estimating the ED50 value of morphine withdrawal jumping induced by naloxone. A significant difference was observed in withdrawal jumping ED50 values among ohmefentanyl stereoisomers. Of these isomers, F9202 and F9204 had similarly potent analgesic action, but very significant difference in naloxone precipitated withdrawal response. Dependent potency index of F9204 was 618-fold weaker than that of F9202. It is concluded that a stereo-structural difference in physical dependence is found to exist among ohmefentanyl stereoisomers. Compound F9204 displayed a strong analgesic action and weak physical dependent potency.