title: Distribution of randomised controlled trials of drugs for post-operative nausea and vomiting.
abstract: OBJECTIVE
  Randomised controlled trials (RCTs) guide therapeutic decisions. But which RCTs are done; which omitted; and which should be done? This study illustrates a method to explore these questions applied to drugs for post-operative nausea and vomiting (PONV).
  
  
  METHODS
  Review articles listed 18 drugs for PONV. All RCTs of these drugs for PONV were sought. The first drug mentioned in an RCT was counted and tabulated against others in all the arms of the RCT (against itself in a dose-ranging RCT). Additional drugs mentioned in these RCTs were added to the study, for a total of 40 drugs.
  
  
  RESULTS
  Drugs involved in the most RCTs were: ondansetron 131 RCTs; propofol 118; droperidol 74; metoclopramide 67; granisetron 52; scopolamine 22; tropisetron 16. Drugs involved in the fewest RCTs: two drugs with 2 RCTs; twelve drugs with one; three with none. Probability that this distribution occurred by chance: P < 0.00001; that the distribution of dose-ranging RCTs occurred by chance: P < 0.001. Regression of RCT numbers on cost: R = 0.86, P < 0.0001; on year of drug introduction: R = 0.14. Of 1600 possible comparisons of drugs for PONV, (including dose-ranging) 97.8% have never been published.
  
  
  CONCLUSIONS
  Although some antiemetic drugs for PONV have been studied in large numbers of RCTs, many have not been adequately evaluated. Finding relevant RCTs and tabulating their comparison arms is useful for directing future research, and is applicable to any symptom or disorder.
authors.affiliation: Department of Anaesthesia, University of Saskatchewan, Royal University Hospital, Saskatoon, Canada. mckayw@sdh.sk.ca
authors.forename: W P
authors.initials: WP
authors.lastname: McKay
authors.forename: R W
authors.initials: RW
authors.lastname: Yip
mesh_terms: D000932:Antiemetics / Q000627:therapeutic use*; D006801:Humans; D020250:Postoperative Nausea and Vomiting / Q000188:drug therapy*; D016032:Randomized Controlled Trials as Topic
chemical_list: D000932:Antiemetics