Dextromethorphan and intrathecal morphine for analgesia after Caesarean section under spinal anaesthesia

Background. Dextromethorphan is an N-methyl-D-aspartic acidantagonist which can attenuate acute pain with few side-effects.In this prospective, randomized, double-blind study of dextromethorphanand intrathecal morphine, we investigated postoperative pain,pruritus, nausea and vomiting in women undergoing Caesareansection under spinal anaesthesia. Methods. Women were allocated randomly to one of six groups,to receive intrathecal morphine 0.05, 0.1 or 0.2 mg plusoral dextromethorphan 60 mg or placebo. Results. The addition of dextromethorphan did not reduce postoperativepain scores (P=0.83). Compared with women receiving intrathecalmorphine 0.05 mg, women receiving higher doses had a significantlyhigher incidence of nausea and vomiting [odds ratio for intrathecalmorphine 0.1 mg, 4.0 (95% confidence interval 1.2–14.1);for intrathecal morphine 0.2 mg, 7.9 (2.3–27.1)].Compared with women receiving intrathecal morphine 0.05 mg,women receiving higher doses also had a significantly higherincidence of pruritus [odds ratio for intrathecal morphine 0.1 mg,3.2 (95% confidence interval 1.3–8.2); for intrathecalmorphine 0.2 mg, 3.7 (1.4–9.5)]. Women receivingdextromethorphan had a lower incidence of nausea and vomiting[odds ratio 2.6 (1.1–6.3)]. Conclusions. Postoperative pain after Caesarean section underspinal anaesthesia was not reduced by the addition of oral dextromethorphanto a multimodal approach including intrathecal morphine. Br J Anaesth 2003; 90: 653–8