The Effect of Opioid Receptor Gene Polymorphism (A118G) on Tramadol Consumption After Caesarean Section

Abstract

Objectives: The efficacy of opioid analgesics is related to the µ-opioid receptor gene. The aim of this study was todetermine the frequency of opioid receptor gene polymorphism at position 118 and response to tramadol for postcesarean analgesia.Methods: We recruited 100 patients aged between 18–45 years, who could use patient-controlled analgesia (PCA) device and express their pain severity with visual rating scale (VRS), and had ASA I-II, undergoing cesarean section underspinal anesthesia. Blood samples were genotyped for the A118G polymorphism-A118 homozygous (AA), heterozygous(AG), or homozygous for the G allele (GG). Pain scores, the severity of nausea and vomiting, other complicaitons and thetotal self-administered intravenous tramadol consumption were recorded for the first 24 postoperative hours.Results: Among the 100 patients in the study, 77 (77%) had a genotype of homozygous 118AA (AA normal), 19 (19%)were heterozygous 118AG (AG), and the remaining four (4%) were genotype homozygous 118GG (GG mutant type).The patients were divided into 3 groups. Compared to that in patients with AG genotype, those with AA homozygousgenotype had significantly higher time to the first analgesic, lower dose of total additional analgesic, and higher patientsatisfaction scores. Nausea and vomiting scores of patients with GG homozygous genotype were significantly higher.Conclusion: In conclusion, A118G polymorphism is associated with variations in tramadol consumption and painscores. The relative rare frequency of the patients who have 118GG homozygous gene within the Turkish populationimplies that it could be safe to use tramadol for postoperative analgesia.