Role of OPRM1 A118G polymorphism in tramadol analgesia following third molar surgery: a pharmacogenomic study.
BACKGROUND: The OPRM1 A118G (rs1799971) polymorphism has been implicated in interindividual variability in opioid analgesic response, but its influence on tramadol efficacy remains uncertain. This study evaluated the association between OPRM1 A118G and postoperative analgesic response to tramadol following mandibular third molar surgery. METHODS: In this prospective pharmacogenomic study, 53 adults undergoing impacted mandibular third molar extraction were enrolled. Genomic DNA was analyzed for OPRM1 A118G (rs1799971) using amplification refractory mutation system polymerase chain reaction (ARMS-PCR). All procedures were performed under 2% lignocaine with adrenaline. Tramadol (50 mg) was administered after the onset of postoperative pain. Pain intensity was assessed using the Visual Analogue Scale (VAS) and Short-Form McGill Pain Questionnaire at 2, 4, and 6 hours. The primary outcome was summed pain intensity difference (SPID, 2-6 hours). RESULTS: Genotype frequencies were in Hardy-Weinberg equilibrium. No significant association was observed between OPRM1 genotype and SPID, VAS reduction, Pain Rating Index change, or responder status during the 6-hour observation period (all p > 0.05). CONCLUSION: OPRM1 A118G was not significantly associated with early tramadol analgesic response following third molar surgery. Larger studies incorporating both OPRM1 and CYP2D6 genotyping are needed to clarify the genetic determinants of tramadol analgesia as CYP2D6 gene is required for tramadol metabolism.