title: Effect of combining ultralow-dose naloxone with morphine in intravenous patient-controlled analgesia: the cut-off ratio of naloxone to morphine for antiemesis after gynecologic surgery.
abstract: OBJECTIVE
  Admixing an ultralow dose of naloxone with intravenous morphine patient-controlled analgesia (PCA) has been shown to decrease postoperative nausea. However, the cut-off ratio of the naloxone-morphine admixture for antiemetic effects has not been investigated. The purpose of this study was to investigate the cut-off ratio of naloxone-morphine admixture in PCA for antiemesis after gynecologic surgery.
  
  
  METHODS
  This double-blind study enrolled 120 female patients who were scheduled for gynecologic surgery under general anesthesia. Patients were randomly allocated to one of three groups (n = 40 for each group). The concentration of naloxone and morphine respectively was 0 microg/mL and 1 mg/mL in group 1, 0.1 microg/mL and 1 mg/mL in group 2 (1:10,000), and 1 microg/mL and 1 mg/mL in group 3 (1:1000). Morphine consumption, verbal rating score of wound pain at rest and with exertion, and morphine-related side effects were investigated at 1, 2, 4 and 24 hours postoperatively.
  
  
  RESULTS
  A total of 112 patients completed the study (37 in group 1, 36 in group 2, 39 in group 3). The incidence of nausea during the postoperative 4-24 hours was significantly lower in group 3 than in group 1 (23.1% vs. 56.8%, p < 0.05). Furthermore, the overall incidence of severe nausea was significantly lower in group 3 than in group 1 (2.6% vs. 24.3%, p < 0.05) as was the rescue antiemetic requirements (5.1% vs. 24.3%, p < 0.05). However, there were no significant differences between groups 2 and 1. The pain scores (at rest and with exertion) and 24-hour morphine consumption were not significantly different among the three groups.
  
  
  CONCLUSIONS
  The antiemetic efficacy of ultralow-dose naloxone combined with PCA morphine is limited by a cut-off ratio of naloxone to morphine of 1:10,000.
authors.affiliation: Department of Anesthesiology, National Taiwan University Hospital, 7 Chung Shan South Road, Taipei, Taiwan.
authors.forename: Yu-Chang
authors.initials: YC
authors.lastname: Yeh
authors.forename: Tzu-Fu
authors.initials: TF
authors.lastname: Lin
authors.forename: Chen-Hua
authors.initials: CH
authors.lastname: Wang
authors.forename: Yong-Ping
authors.initials: YP
authors.lastname: Wang
authors.forename: Chen-Jung
authors.initials: CJ
authors.lastname: Lin
authors.forename: Wei-Zen
authors.initials: WZ
authors.lastname: Sun
mesh_terms: D016058:Analgesia, Patient-Controlled / Q000379:methods*; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D009020:Morphine / Q000008:administration & dosage*; D009270:Naloxone / Q000008:administration & dosage*; D009292:Narcotic Antagonists / Q000008:administration & dosage*; D020250:Postoperative Nausea and Vomiting / Q000517:prevention & control*
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009270:Naloxone; D009020:Morphine