In reply

Abstract

We thank Drs Tan and Sia for their comments regarding our labor and postcesarean analgesia studies of polymorphism (304A>G) at the mu-opioid receptor (OPRM1). 1 Wong C.A. McCarthy R.J. Blouin J. Landau R. Observational study of the effect of mu-opioid receptor genetic polymorphism on intrathecal opioid labor analgesia and post-cesarean delivery analgesia. Int J Obstet Anesth. 2010; 19: 246-253 Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar We designed the study to identify differences in pain outcomes between women homozygous for the wild-type allele (304AA) and women hetero- or homozygous for the mutant allele because a previous study by one of us (R.L.) found a significant difference in the ED50 for intrathecal fentanyl for labor analgesia between these two groups. 2 Landau R. Kern C. Columb M.O. Smiley R.M. Blouin J.L. Genetic variability of the mu-opioid receptor influences intrathecal fentanyl analgesia requirements in laboring women. Pain. 2008; 139: 5-14 Abstract Full Text Full Text PDF PubMed Scopus (124) Google Scholar As acknowledged in our paper, our negative results differ from those of a study performed in Singapore in a Han Chinese population by Drs Sia and Tan’s group. 3 Sia A.T. Lim Y. Lim E.C. et al. A118G single nucleotide polymorphism of human mu-opioid receptor gene influences pain perception and patient-controlled intravenous morphine consumption after intrathecal morphine for postcesarean analgesia. Anesthesiology. 2008; 109: 520-526 Crossref PubMed Scopus (240) Google Scholar When we analyzed our data using the three groups suggested by Drs Tan and Sia (304AA, 304AG, 304GG) there was no difference among the groups in either of our studies. However, the studies were not powered to make these comparisons. Observational study of the effect of μ-opioid receptor genetic polymorphism on intrathecal opioid labor analgesia and post-cesarean delivery analgesiaInternational Journal of Obstetric AnesthesiaVol. 19Issue 3PreviewThe purpose of this two-part prospective observational and blinded trial was to determine whether the single nucleotide polymorphism of the μ-opioid receptor gene (OPRM1:c.304A>G) modifies (1) the duration of intrathecal fentanyl labor analgesia and (2) supplemental analgesic requirements after intrathecal morphine analgesia following cesarean delivery. Full-Text PDF Effect of OPRM variant on labor analgesia and post-cesarean delivery analgesiaInternational Journal of Obstetric AnesthesiaVol. 19Issue 4PreviewWe read with interest the report by Wong et al. which concluded that there was no association between intrathecal opioid analgesia and OPRM1 variant G allele (118A>G or N40D).1 It is a commendable effort which aimed to examine the association of the polymorphism with the duration of intrathecal fentanyl in labouring women and the amount of rescue analgesia for the 72 h following intrathecal morphine injection for planned cesarean deliveries. Full-Text PDF