Observational study :the effect of µ-Opioid receptor genetic polymorphism on neuraxial opioid labor analgesia -

Abstract

Introduction Opioids are commonly used to relieve labor pain, the most painful episode a woman could experience in her life. However the treatment with opioids is associated with a wide interindividual variability in efficacy. As mu-opioid receptor (OPRM1) is known to modulate pain perception and mediate the analgesic effect of opioids in the central nervous system, we examined the effect of A118G polymorphism on the duration of analgesia following epidural fentanyl analgesia during labor.Methods Twenty five nulliparous females were recruited prospectively during normal vaginal delivery necessitating epidural anesthesia, and genotyped for A118G polymorphism using allele discrimination assay by real time PCR. Outcomes included duration of fentanyl analgesia, pain scores, and need for additional doses of local anesthetics and fentanyl.Results The minor allele frequency (MAF) of allele G was 12percent, and the genotype frequencies were in Hardy Weinberg Equilibrium. Female participants carrying the G allele required significantly higher doses of additional lidocaine [147±68 mg] as compared with the wild types [63.5±53.8mg] (P=0.015). Furthermore, survival analysis showed a trend towards a shorter duration of fentanyl analgesia in mutant allele carriers (P=0.077). In addition, a trend was observed with the visual analogue scale (VAS) such that carriers of G allele seemed to have higher pain scores (P=0.097).Conclusion Despite the small sample size, results demonstrated that OPRM 118G variant was associated with significantly increased requirement for manual lidocaine and a trend towards higher pain scores as well as shorter duration of fentanyl analgesia. Further recruitment is ongoing to enhance the power of the study. These findings, if validated, may have implications for patients receiving opioid therapy during delivery and in other settings.