RESUMEN
Dextromethorphan [DM], the D-isomer of the codeine analogue levorphanol, is a weak, noncompetitive N-Methyl-D-Aspartate [NMDA] receptor antagonist. It has been suggested that NMDA receptor antagonists induce preemptive analgesia when administrated before tissue injury occurs, thus decreasing the subsequent sensation of pain. The study was conducted in the Dr Ali Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. In this seventy two patients scheduled for elective cholesyctectomy between February 2005 and December 2006 were randomized into three equal groups to receive as premedication either oral dextromethorphan 45 mg [Group D45 = 24], dextromethorphan 90 mg [Group D 90 = 24] or placebo [Group C, n = 24], 120 min before surgery. A visual analogue scale [VAS] for pain of each patient measured at arrival in the ward and 6 and 24 hours after surgery, was recorded. The demographic characteristics of patients, ASA physical status class, duration of surgery, and the basal VAS pain score were similar in the two groups. There was no significant difference in the mean of the VAS pain scores measured over time or morphine consumption between three groups. Dextromethorphan, 45 and 90 mg orally administrated 2 h before surgery had no effect on postoperative morphine requirement and pain intensity