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

Background: Dextromethorphan is an N-methyl-D-aspartic acid antagonist which can attenuate acute pain with few side-effects. In this prospective, randomized, double-blind study of dextromethorphan and intrathecal morphine, we investigated postoperative pain, pruritus, nausea and vomiting in women undergoing Caesarean section 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 plus oral dextromethorphan 60 mg or placebo.

Results: The addition of dextromethorphan did not reduce postoperative pain scores (P=0.83). Compared with women receiving intrathecal morphine 0.05 mg, women receiving higher doses had a significantly higher incidence of nausea and vomiting [odds ratio for intrathecal morphine 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 higher incidence of pruritus [odds ratio for intrathecal morphine 0.1 mg, 3.2 (95% confidence interval 1.3-8.2); for intrathecal morphine 0.2 mg, 3.7 (1.4-9.5)]. Women receiving dextromethorphan had a lower incidence of nausea and vomiting [odds ratio 2.6 (1.1-6.3)].

Conclusions: Postoperative pain after Caesarean section under spinal anaesthesia was not reduced by the addition of oral dextromethorphan to a multimodal approach including intrathecal morphine.