We examined the
analgesic effect of racemic
ketamine and its 2 enantiomers in 16 female patients (age: 20-29 years) suffering
acute pain after
oral surgery and in 7 female patients (age: 42-79 years) suffering chronic neuropathic
orofacial pain. All 3 forms of
ketamine consistently relieved
postoperative pain, (
S)-ketamine being 4 times more potent than (R)-
ketamine. The
analgesic effect was maximal 5 min after i.m. injection and lasted for about 30 min. The 7 patients with
neuropathic pain received
ketamine at one or several occasions. Four patients (age: 54-79 years) who had suffered
pain for more than 5 years did not experience an
analgesic effect, whereas 3 patients (age: 42-53 years) who had suffered
pain for less than 3 years reported
pain relief lasting from 24 h to 3 days. The individual type of response did not depend on the form of
ketamine used. The mental side effects were qualitatively similar for the 3 forms of
ketamine. Relative to the
analgesic effect (
S)-ketamine caused more disturbing side effects than did (R)-
ketamine. The mean serum concentration of each form of
ketamine at the time of maximal effect was close to the approximate Kd value for PCP site occupancy by that particular form. This is in concert with the hypothesis that the effect of
ketamine on acute
nociceptive pain is due to
N-methyl-D-aspartate (
NMDA) receptor inhibition and adds to the evidence that
NMDA receptors are important for the perception of acute,
nociceptive pain in humans.(ABSTRACT TRUNCATED AT 250 WORDS)