Preoperative dextromethorphan reduces intraoperative but not postoperative morphine requirements after laparotomy

N-methyl-D-aspartate (NMDA) antagonists combined with opioids are thought to be effective in the control of pain states. We evaluated morphine use and analgesia in 37 patients postlaparotomy. Patients received 60 mg of oral dextromethorphan or placebo the night before and again 1 h before surgery. Morphine was titrated intraoperatively to maintain blood pressure and heart rate within 20% of baseline and postoperatively via patient-controlled analgesia (PCA). The dextromethorphan and placebo groups were compared for morphine use intraoperatively, in recovery, via PCA in the first 4 and 24 h, and total use over the study period. Pain scores at rest and on activity for the first 4 and 24 h were also compared. Intraoperatively, the dextromethorphan group required less morphine: 13.1+/-4.3 vs 17.6+/-6.0 mg (P = 0.012). Postoperatively, there was no significant difference between the dextromethorphan and placebo groups for morphine use: in the recovery room 10.9+/-7.7 vs 12.1+/-7.7 mg; the first 4 h of PCA 15.9+/-9.3 vs 12.7+/-5.1 mg; the first 24 h of PCA 76.4+/-44.7 vs 61.8+/-27.5 mg; or in total morphine use 100.4+/-49.5 vs 91.5+/-3.1 mg. Pain scores for the two groups were not statistically different throughout the study period. We conclude that 60 mg of oral dextromethorphan given the night before and repeated an hour before surgery does not provide a postoperative morphine-sparing effect or improve analgesia after laparotomy.

Patients given dextromethorphan before surgery had significantly reduced intraoperative morphine requirements. However, postoperative morphine requirements were unaltered. Dextromethorphan may need to be continued postoperatively to improve postoperative analgesia.