The effect of dextromethorphan, alone or in combination with ibuprofen, on postoperative pain after minor gynaecological surgery

Background: Experimental studies have demonstrated that peripheral tissue injury may lead to hyperexcitability of nociceptive neurones in the dorsal horn, in part mediated by N-methyl-D-aspartate (NMDA)-receptor mechanisms. Sensitisation of dorsal horn neurones may be an important contributor to postoperative pain. The aim of the present study was to investigate the effect of the NMDA-receptor antagonist dextromethorphan on pain after minor gynaecological surgery, and to evaluate a potential additive effect with ibuprofen. Methods: In a double-blind, placebo-controlled study, 100 patients scheduled for elective termination of pregnancy were randomised to receive placebo, oral ibuprofen 400 mg, oral dextromethorphan 120 mg, or a combination of ibuprofen 400 mg and dextromethorphan 120 mg, 1 h before surgery. Pain and analgesic requirements were assessed 0.5, 1 and 2 h after operation. Results: We observed no effect of dextromethorphan on visual analogue scale (VAS) pain scores or analgesic consumption, and no additive or synergistic analgesic effects between ibuprofen and dextromethorphan. Ibuprofen reduced pain scores compared with placebo, and analgesic consumption compared with both placebo and dextromethorphan. The combination of ibuprofen and dextromethorphan increased preoperative nausea compared with both placebo and ibuprofen, whereas no statistically significant side effects were observed with dextromethorphan alone. Conclusion: No analgesic effects of oral dextromethorphan 120 mg on pain after surgical termination of labour, and no additive analgesic effects when combined with ibuprofen 400 mg, were observed. Ibuprofen reduced both VAS pain scores and analgesic consumption compared with placebo.