Human opioid receptor A118G polymorphism affects intravenous patient-controlled analgesia morphine consumption after total abdominal hysterectomy.

Background: Animal and human studies indicate that genetics may contribute to the variability of morphine efficacy. A recent report suggested that cancer patients homozygous for the 118G allele caused by the single nucleotide polymorphism at nucleotide position 118 in the mu-opioid receptor gene require higher doses of morphine to relieve pain. The purpose of the current study was to investigate whether this polymorphism contributes to the variability of morphine efficacy in women who undergo abdominal total hysterectomy.

Methods: After informed consent was obtained, 80 female patients (American Society of Anesthesiologist physical status I or II) scheduled to undergo elective total hysterectomy surgery were enrolled in this study. All patients received general anesthesia and were screened for A118G polymorphism by blood sample. Intravenous morphine patient-controlled analgesia was provided postoperatively for satisfactory analgesia. The authors recorded the morphine consumption doses and demand times. Pain at rest and side effects were measured with rating scales.

Results: Forty-three women were A118 homozygous, 19 were heterozygous, and 18 were G118 homozygous. Patients homozygous for G118 required more morphine doses (33 +/- 10 mg) to achieve adequate pain relief compared with patients homozygous for A118 (27 +/- 10 mg) in the first 24 h (P = 0.02). However, there was no statistically significant difference for morphine consumption at 48 h.

Conclusion: Genetic variation of the mu-opioid receptor may contribute to interindividual differences in postoperative morphine consumption. In the future, identifying single nucleotide polymorphisms of patients may provide information to modulate the analgesic dosage of opioid for better pain control.