Psychotomimetic effects of subanesthetic doses of ketamine: Dose versus effect relationships
Psychotomimetic emergence phenomena following general anesthesia with ketamine are well documented, and affect 5-30% of patients. The psychotomimetic effects of subanesthetic doses of ketamine have been less well studied. We administered ketamine or saline in single blinded, crossover fashion to 10 psychiatrically healthy volunteers using a computer-assisted continuous ketamine infusion that achieved a stepwise series of 5 constant plasma levels of ketamine, at 0, 5, 10, 15, and 20 jug/ml. After approximately 20 min at each level, to allow for equilibration with the biophase, the volunteer completed a visual analog rating of 13 psychotic and dissociative symptom scales involving color, reality, sounds, body parts, ideas of reference, surroundings, time, euphoria, out-of-control thoughts, anxiety, drowsiness and suspiciousness. Target ketamine levels were verified by measuring actual plasma concentration. Ketamine produced marked psychotomimetic effects that were doserelated in a highly linear fashion for all scales (r 0.92; p 0.03). Effects on anxiety, suspiciousness, and ideas of reference were weakest, attaining less than 22% of the maximum possible effect. For all other scales, 37-89% of the maximum possible effect was attained.
