SummaryWhat is known and objective: Pruritus is one of the most common adverse effects associated with neuraxial morphine. Ondansetron has been used to deal with the problem of neuraxial morphine-induced pruritus (NMIP). The aim of this meta-analysis was to evaluate the preventive efficacy of ondansetron on NMIP. Methods: Online databases such as PubMed, EMBASE and the Cochrane CentralRegister of Controlled Trials were searched for eligible randomized controlled trials (RCTs). The primary outcome was the incidence of NMIP. We calculated risk ratios (RR) with 95% confidence intervals (CI) for dichotomous data. Trial sequential analysis (TSA) was performed to avoid the risk of making a spurious claim of significant effect and to calculate the sample size necessary to make a robust claim of effect. Results and discussion:Our traditional meta-analysis showed that prophylactic ondansetron could significantly reduce the incidence of NMIP in non-obstetric patients (three trials, RR=0.63, 95% CI 0.45-0.89, P=.008) with modest heterogeneity (I 2 =47%)while it did not show the preventive efficacy of NMIP in obstetric patients (seven trials, RR=0.84, 95% CI 0.69-1.03, P=.10) with obvious heterogeneity (I 2 =82% ). However, TSA demonstrates that more high-quality RCTs are still needed to confirm the preventive efficacy of ondansetron on NMIP in non-obstetric populations and to study whether ondansetron prevents NMIP in obstetric patients.What is new and conclusion: Prophylactic ondansetron can significantly reduce the incidence of NMIP in non-obstetric patients but not in obstetric patients. However, more well-designed trials are still required to test the reliability of the results in our traditional meta-analysis. K E Y W O R D Sclinical pharmacy, meta-analysis, morphine, ondansetron, pruritus to be applied in meta-analyses to assess the reliability of the evidence in traditional meta-analysis and provide the sample size necessary to make a robust claim of effect (termed as the required information size, RIS). 10,11 Therefore, we performed this study to evaluate the preventive efficacy of ondansetron on neuraxial morphine-induced pruritus. | WHAT IS KNOWN AND OBJECTIVE | METHODS This meta-analysis was conducted according to the PreferredReporting Items for Systematic Reviews and Meta-analyses (PRISMA)guidelines. 12 | Search strategyThree databases such as PubMed, EMBASE and the Cochrane CentralRegister of Controlled Trials were searched with language restriction to English for randomized controlled trials (RCTs) assessing the preventive effectiveness of ondansetron on NMIP. Besides, we also manually screened the reference lists of relevant reviews and studies for eligible articles. The search strategies for the three online databases were given in Appendix S1. The last search was conducted on 10 March 2017. | Eligibility criteria and study selectionFull-text RCTs published in English that compared the preventive efficacy of intravenous ondansetron versus control (namely, 0.9% normal saline) on pruritus induced by neuraxia...