Comparative pharmacology of the optical isomers of ketamine in mice

Relative pharmacological potencies of the optical isomers of ketamine have been estimated in ICR mice. The (+)-isomer was 3X more potent than (-)-ketamine as an analgesic using the phenylquinone writhing test, only 1.5X more potent in terms of hypnotic activity and 1.8X more potent in causing locomotor stimulation. At equianalgesic doses (+)-ketamine caused less stimulation of locomotor activity than the (-)-isomer. These potency differences did not appear to be due to differences in biodisposition although stereoselective metabolism was demonstrated in vivo. Analgesia induced by ketamine was reversed by 10 mg/kg of naloxone.