title: OPRM1 A118G gene variant and postoperative opioid requirement: a systematic review and meta-analysis.
abstract: BACKGROUND
  Although a number of studies have investigated the association of the OPRM1 A118G polymorphism with pain response, a consensus has not yet been reached.
  
  
  METHODS
  The authors searched PubMed, EMBASE, and the Cochrane Library to identify gene-association studies that explored the impact of the OPRM1 A118G polymorphism on postoperative opioid requirements through July 2013. Two evaluators independently reviewed and selected articles on the basis of prespecified selection criteria. The authors primarily investigated the standardized mean difference (SMD) of required amounts of opioids between AA homozygotes and G-allele carriers. The authors also performed subgroup analyses for race, opioid use, and type of surgery. Potential bias was assessed using the Egger's test with a trim and fill procedure.
  
  
  RESULTS
  Three hundred forty-six articles were retrieved from databases, and 18 studies involving 4,607 participants were included in the final analyses. In a random-effect meta-analysis, G-allele carriers required a higher mean opioid dose than AA homozygotes (SMD, -0.18; P = 0.003). Although there was no evidence of publication bias, heterogeneity was present among studies (I(2) = 66.8%). In the subgroup meta-analyses, significance remained robust in Asian patients (SMD, -0.21; P = 0.001), morphine users (SMD, -0.29; P <0.001), and patients who received surgery for a viscus (SMD, -0.20; P = 0.008).
  
  
  CONCLUSIONS
  The OPRM1 A118G polymorphism was associated with interindividual variability in postoperative response to opioids. In a subpopulation, identifying OPRM1 A118G polymorphism may provide valuable information regarding the individual analgesic doses that are required to achieve satisfactory pain control.
authors.affiliation: From the Department of Family Medicine, Gachon University Gil Medical Center, Incheon, Republic of Korea (I.C.H.); Department of Clinical Pharmacology and Toxicology, Anam Hospital, Korea University College of Medicine, Seoul, Republic of Korea (J.-Y.P.); Molecular Epidemiology Branch, Research Institute, National Cancer Center, Goyang, Republic of Korea (S.-K.M.); Department of Statistics, Dongguk University, Seoul, Republic of Korea (H.Y.A.); Division of Dental Anesthesiology, Department of Oral Health and Clinical Science, Tokyo Dental College, Suidoubashi Hospital, Tokyo, Japan (K.-i.F.); and Department of Anesthesiology, The Third Xiangya Hospital of Central South University, Changsha, China (Q.L.).
authors.forename: In Cheol
authors.initials: IC
authors.lastname: Hwang
authors.forename: Ji-Young
authors.initials: JY
authors.lastname: Park
authors.forename: Seung-Kwon
authors.initials: SK
authors.lastname: Myung
authors.forename: Hong Yup
authors.initials: HY
authors.lastname: Ahn
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Fukuda
authors.forename: Qin
authors.initials: Q
authors.lastname: Liao
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000818:Animals; D014644:Genetic Variation / Q000235:genetics*; D006801:Humans; D010149:Postoperative Pain / Q000188:drug therapy / Q000235:genetics*; D011182:Postoperative Care / Q000379:methods; D017450:Receptors, Opioid, mu / Q000235:genetics*
chemical_list: D000701:Analgesics, Opioid; C485764:OPRM1 protein, human; D017450:Receptors, Opioid, mu