What is "nortilidine"

Nortilidine is the major active metabolite of tilidine. It is formed from tilidine by demethylation in the liver. The racemate has opioid analgesic effects roughly equivalent in potency to that of morphine but virtually all of the opioid activity resides in the (1S,2R) isomer. The (1R,2S) isomer has NMDA antagonist activity. The drug also acts as a dopamine reuptake inhibitor. The reversed-ester of tilidine is also known which has almost identical properties to nortilidine.