Summary

Background and objective: There is a controversy regarding the best drug for prevention of nausea and vomiting in patients receiving intrathecal morphine. The aim of this study was to examine efficacy and tolerability of droperidol compared with ondansetron for the prevention of morphine-induced nausea and vomiting. Methods: In a randomized, placebo-controlled trial, 120 women undergoing Caesarean section under spinal anaesthesia with intrathecal morphine 0.1 mg received intravenous ondansetron 4 mg (n = 40), droperidol 1.25 mg (n = 40) or saline (n = 40) immediately after umbilical-cord clamping. Nausea and vomiting were graded according to intensity at 1, 2, 4, 6, 12 and 24 h. Results: Nausea or vomiting occurred in 14 patients (35%) in the placebo group, 4 (10%) in the ondansetron group and 10 (25%) in the droperidol group; the difference between ondansetron and placebo was statistically significant (P = 0.007). Eleven of the 14 placebo patients (27.5%) vomited, compared with none of the 4 ondansetron patients (vs. placebo, P = 0.0004) and 5 of the droperidol patients (vs. placebo, P = 0.18). Three of the 14 placebo patients (7.5%) were nauseous, compared with 4 (10%) receiving ondansetron and 5 (12.5%) receiving droperidol. Conclusions: Ondansetron was effective in reducing the incidence of nausea and vomiting in patients receiving intrathecal morphine for Caesarean section.

Summary

Background and objective: The clinical practice of spinal morphine administration for pain relief is based on observations in animals that opioid receptors exist in the spinal cord and intrathecal injections of opioids in those species (mostly rats) lead to antinociceptive effects. Clinicians are well aware that administration of spinal opioids is associated with side-effects, such as nausea and respiratory depression, that indicate supraspinal spread of the drug administered. Those observations call into question how much of the observed pain relief is due to action of the drug in the brain. This study investigated the spinal cord actions of morphine given intrathecally to rats in a model that allows investigation of drug–receptor interaction at the spinal cord level. Experiments were performed on male Wistar rats with chronically implanted lumbar subarachnoid catheters.

Methods: Nociceptive thresholds were measured in rats given morphine intrathecally alone and in combination with intrathecal injections of selective opioid receptor antagonists: β-funaltrexamine (μ), naltrindole (δ) and nor-binaltorphimine (κ).

Results: Intrathecal morphine caused dose-related antinociceptive effects that were reversed totally by naloxone. Intrathecal β-funaltrexamine and naltrindole did not reverse the effects of intrathecal morphine. However, intrathecal nor-binaltorphimine did reverse the electrical current threshold effects of morphine but not tail flick latency.

Conclusions: Antinociception following intrathecal morphine involves spinal and supraspinal opioid receptors. The tail flick effect described in rat experiments involves actions at opioid receptors in the brain that override any action that may be caused by combination of morphine with μ-opioid receptors in the spinal cord.