Abstract: Objective To investigate whether A118G single nucleotide polymorphisms of the μ-opioid receptor (OPRM1) affects
epidural patient-controlled analgesia with fentanyl after caesarian section. Methods A total of 100 pregnant women (ASA class
I or II) scheduled for elective caesarian section were enrolled in this study. All the patients received spinal-epidural anesthesia
and were screened for blood A118G polymorphism. Epidural patient-controlled analgesia with fentanyl was provided
postoperatively. The pain scores, incidence of nausea and vomiting, and total self-administered epidural fentanyl dose within
48 h postoperatively were recorded. Results Ninety-six patients were finally included in this study. The percentages of the
genotypes AA, AG, and GG were 36.5% (35 cases), 46.9% (45 cases), and 16.7% (16 cases), respectively. At 12 and 24 h
postoperatively, the pain scores and the total fentanyl dose administered were significantly higher in group GG than in groups
AA and AG. Conclusion A118G single nucleotide polymorphism affects pain relief and total fentanyl dose administered in
epidural patient-controlled analgesia after caesarian section. G118 homozygotes have a poorer response to fentanyl than A118
homozygotes or heterzygotes.