Ketamine retards chronic but not acute tolerance to ethanol.

Motor impairment (tilt-plane test) was used to investigate whether the noncompetitive N-methyl-D-aspartate (NMDA) antagonist ketamine prevents the development of chronic and acute tolerance to ethanol. Rats were treated with ethanol or saline in the presence and absence of ketamine (separate groups) for 10 days and tested for ethanol tolerance in the absence of ketamine on the fifth and tenth days. In other studies, the effect of ketamine on acute tolerance to ethanol was examined. Rats that received ethanol daily without ketamine showed significant tolerance to ethanol on days 5 and 10, but those receiving ethanol plus ketamine daily showed significantly less tolerance to ethanol. Thus, ketamine interfered with the development of chronic tolerance just as it had been found previously to prevent rapid tolerance. In contrast, ketamine failed to block acute tolerance to ethanol. These results would suggest that the phenomena of acute tolerance and chronic tolerance have differences not previously reported.