FIGURE 1.

Metabolic pathway of ketamine enantiomers. (S)-ketamine and (R)-ketamine are a pair of stereoisomers. In vivo, (S)-ketamine and (R)-ketamine is initially demethylated to (S)-norketamine or (R)-norketamine. (S)-norketamine or (R)-norketamine is further metabolized to (S)-DHNK or (R)-DHNK. (S)-norketamine or (R)-norketamine can also be hydroxylated into (2S,6S)-HNK or (2R,6R)-HNK, respectively. Recently, ketamine and several of its metabolites with potential antidepressant-like effects have intrigued enthusiastic investigations at preclinical and clinical levels. Abbreviations: (2R,6R)-HK, (2R,6R)-hydroxyketamine; (2S,6S)-HK, (2S,6S)-hydroxyketamine; (2R,6R)-HNK, (2R,6R)-hydroxynorketamine; (2S,6S)-HNK, (2S,6S)-hydroxynorketamine; (R)-DHNK, (R)-dehydronorketamine; (S)-DHNK, (S)-dehydronorketamine.