title: Effects of OPRM1 A118G polymorphism on epidural analgesia with fentanyl during labor: a meta-analysis.
abstract: BACKGROUND
  Emerging evidence has shown that the most common polymorphism (A118G; rs1799971 A>G) in the μ-opioid receptor (OPRM1) gene may influence the response to labor analgesia, but individually published studies showed inconclusive results.
  
  
  OBJECTIVE
  This meta-analysis aimed to derive a more precise estimation of the effects of the OPRM1 A118G polymorphism on epidural analgesia with fentanyl during labor.
  
  
  METHODS
  A literature search was conducted on PubMed, Embase, Web of Science, and China BioMedicine databases before April 1st, 2013. The crude standardized mean difference (SMD) or odds ratio (OR) with 95% confidence interval (CI) was calculated.
  
  
  RESULTS
  Six clinical studies were included with a total 838 women who received epidural analgesia with fentanyl during labor. The meta-analysis results indicated that women carrying the G allele (AG+GG) of the OPRM1 A118G polymorphism required less fentanyl doses to achieve adequate pain relief compared with those with the AA homozygote (SMD=-0.24, 95% CI [-0.44, -0.03], p=0.022). The 118G variant was associated with a decreased ED50 of fentanyl for labor analgesia (SMD=-1.56, 95% CI [-1.97, -1.15], p<0.001). The analgesia satisfaction in women carrying the G allele (AG+GG) was higher than those with the AA homozygote (SMD=0.22, 95% CI [0.05, 0.39], p=0.012). However, there were no statistically significant differences between an AA homozygote and a G carrier (AG+GG) in the incidence of nausea and vomiting (OR=1.99, 95% CI [0.88, 4.52], p=0.101).
  
  
  CONCLUSIONS
  In conclusion, the current meta-analysis indicates that women carrying the G allele (AG+GG) of OPRM1 A118G polymorphism may have a good response to epidural analgesia with fentanyl during labor. The OPRM1 A118G polymorphism may help predict individuals' response to epidural labor analgesia and so optimize postoperative pain control.
authors.affiliation: 1 Department of Anesthesiology, Changzheng Hospital, Second Military Medical University , Shanghai, China .
authors.forename: Zheming
authors.initials: Z
authors.lastname: Song
authors.forename: Boxiang
authors.initials: B
authors.lastname: Du
authors.forename: Kai
authors.initials: K
authors.lastname: Wang
authors.forename: Xueyin
authors.initials: X
authors.lastname: Shi
mesh_terms: D000483:Alleles; D015360:Analgesia, Epidural; D000701:Analgesics, Opioid / Q000627:therapeutic use*; D002986:Clinical Trials as Topic; D005260:Female; D005283:Fentanyl / Q000627:therapeutic use*; D006720:Homozygote; D006801:Humans; D007743:Labor, Obstetric / Q000187:drug effects / Q000235:genetics*; D010149:Postoperative Pain / Q000188:drug therapy / Q000235:genetics*; D011110:Polymorphism, Genetic; D011247:Pregnancy; D039781:PubMed; D017450:Receptors, Opioid, mu / Q000235:genetics*
chemical_list: D000701:Analgesics, Opioid; C485764:OPRM1 protein, human; D017450:Receptors, Opioid, mu; D005283:Fentanyl