Morphine-induced pruritus after spinal anaesthesia

Abstract

Editor—I read with interest the study by Horta and colleagues1Horta ML Morejon LCL da Cruz AW et al.Study of the prophylactic effect of droperidol, alizapride, propofol and promethazine on spinal morphine-induced pruritus.Br J Anaesth. 2006; 96: 796-800Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar in which they compared the prophylactic effect of droperidol, alizapride, propofol and promethazine on spinal morphine-induced pruritus. Another group of drugs that have been found to be useful in this setting but not included in the study are 5-hydroxytryptamine subtype 3 (5-HT3) receptor antagonists such as ondansetron and dolasetron. One of the postulated mechanisms of intrathecal opioid-induced pruritus is a direct excitatory effect of the opioid on the dorsal horn. High concentrations of 5-HT3 receptors have been located in the dorsal part of the spinal cord, especially in the superficial layers of the dorsal horn, and in the nucleus of the spinal tract of the trigeminal nucleus, in animal studies.2Borgeat A Stirnemann HR Ondansetron is effective to treat spinal or epidural morphine-induced pruritus.Anaesthesiology. 1999; 90: 432-436Crossref PubMed Scopus (91) Google Scholar This indicates that opioids might cause pruritus by activating central 5-HT3. There are few studies on the effectiveness of 5-HT3 antagonists reported, and these have provided conflicting results. A study by Iatrou and colleagues3Iatrou CA Dragoumanis CK Vogiatzaki TD Vretzakis GI Simopoulos CE Dimitriou VK Prophylactic intravenous ondansetron and dolasetron in intrathecal morphine-induced pruritus: a randomized, double-blind, placebo-controlled study.Anaesth Analg. 2005; 101: 1516-1520Crossref PubMed Scopus (44) Google Scholar showed a decreased incidence and severity of pruritus with the use of ondansetron and dolasetron in patients undergoing urological, orthopaedic or vascular surgery using intrathecal morphine. A similar result was obtained by Charuluxananan and colleagues.4Charuluxananan S Somboonviboon W Kyokong O Nimcharoendee K Ondansetron for the treatment of intrathecal morphine-induced pruritus after caesarean delivery.Reg Anesth Pain Med. 2000; 25: 535-539Crossref PubMed Google Scholar On the other hand, a recent study5Sarvela PJ Halonen PM Soikkeli AI Kainu JP Korttila KT Ondasetron and tropisteron do not prevent intraspinal morphine- and fentanyl-induced pruritus in elective caesarean section.Acta Anaesthesiol Scand. 2006; 50: 239-244Crossref PubMed Scopus (45) Google Scholar did not show any reduction in pruritus with ondansetron in patients undergoing elective caesarean section with intrathecal morphine and i.v. fentanyl. Most of the studies have compared the efficacy of a 5-HT3 receptor antagonist with a placebo and not to other drugs. It would be interesting to compare the efficacy of a 5-HT3 receptor antagonist such as ondansetron to the rest of the drugs.