Influence of OPRM1 Polymorphism on Postoperative Pain After Intrathecal Morphine Administration in Italian Patients Undergoing Elective Cesarean Section

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Objectives:The aim of this prospective observational study was to evaluate the influence of OPRM1 polymorphism on the analgesic efficacy (including visual analog scale [VAS] scores and requirement for rescue analgesia) of a standard dose of intrathecal morphine.Materials and Methods:An Italian cohort of 63 parturients, scheduled for elective cesarean section at a tertiary University Hospital, received spinal anesthesia with hyperbaric bupivacaine and morphine 100 mcg. For the first 48 hours in the postoperative period the patients received acetaminophen 1 g IV q6hr. Incident pain was treated with ketorolac 30 mg IV. Every 6 hours the following parameters were registered: VAS at rest, VAS during movements, postoperative nausea and vomiting, pruritus, and rescue analgesic medications requirements. Age and anthropometric data, number of pregnancies, educational level, OPRM1 genotype, were also obtained.Results:Of the 63 patients enrolled, 45 (71%) were homozygous genotype A/A (118A group), whereas 18 carried the G variants of OPRM1 (A/G or G/G) (118G group). No significant differences in analgesic rescue doses’ administration and in incidence of moderate/severe postoperative pain (VAS>3) between the 2 groups were observed. Pruritus was more frequent in the 118A group than in the 118G group in the first 24 hours of the postoperative period.Discussion:In the Italian population participating in this study there was a different incidence of pruritus in the postcesarean period in response to intrathecal opioids related to OPRM1 gene polymorphism, but not of postoperative pain.

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