OBJECTIVETo investigate whether A118G single nucleotide polymorphisms of the µ-opioid receptor (OPRM1) affects epidural patient-controlled analgesia with fentanyl after caesarean section.

METHODSA total of 100 pregnant women (ASA class I or II) scheduled for elective caesarean 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.

RESULTSNinety-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.

CONCLUSIONA118G single nucleotide polymorphism affects pain relief and total fentanyl dose administered in epidural patient-controlled analgesia after caesarean section. G118 homozygotes have a poorer response to fentanyl than A118 homozygotes or heterozygotes.