OPRM1 A118G gene polymorphism and interindividual differences in postoperative nausea and vomiting induced by IV tramadol in patients undergoing femur fracture surgery- A pilot study.

BACKGROUND AND AIMS: The opioid receptor mu receptor 1(OPRM1) gene codes the human μ-opioid receptor, which is a major target for opioids. The OPRM1 A118G polymorphism leads to inter-individual variation in the susceptibility to postoperative nausea and vomiting (PONV). This study explored the OPRM1 A118G gene polymorphism and inter-individual differences in PONV induced by postoperative IV tramadol in patients undergoing femur fracture surgery.

MATERIAL AND

METHODS

The present prospective observational study was conducted following IEC approval, prospective CTRI registration, and written informed consent. Patients of ASA PS I/II undergoing femur fracture surgery under subarachnoid block were included. Fifty patients of ASA I and II, aged 18-60 years, of either sex, undergoing isolated femur fracture surgery and receiving IV tramadol postoperatively were included. Two milliliters venous sample was withdrawn for gene polymorphism study preoperatively. Incidence of PONV and comparison of PONV score, total rescue antiemetic consumption, postoperative NRS pain score, and total analgesic consumption were compared between different genotypes in the first 24 h postoperatively.

RESULTS

The prevalence of the wild homozygous allele (AA) was 56%, and mutant-G alleles, i.e., AG and GG, were 36% and 8%, respectively. PONV incidence was significantly higher in the AA allele than in mutant-G alleles i.e. 89% vs 7%; odd's ratio is 0.214 (P value = 0.000097), reflecting the protective role of the G allele in patients' predisposition to PONV. Patients with AA allele of OPRM1 A118G required significantly more rescue antiemetic in the first 24h postoperatively.

CONCLUSION

A significantly lower incidence of PONV and lower consumption of rescue antiemetics was observed among patients with mutant G alleles of OPRM1 A118G.