Polymorphism of the micro-opioid receptor gene (OPRM1 118AG) affects fentanyl-induced analgesia during anesthesia and recovery

Background: There is much variation in the response of both individuals and different ethnic populations to opioids, with genetic differences being responsible for interindividual variation. The m-opioid receptor single nucleotide polymorphism (rs number 1799971) at nucleotide position 118 (OPRM1 118A>G) affects the analgesic response to opioids. Objective: This study aimed to investigate the association between the OPRM1 118A>G polymorphism and the effects of fentanyl-induced analgesia, respiratory depression, and anesthetic recovery responses in a population of Han Chinese patients. Study Design: The study was a case series in a hospital setting, with 1 year of study and 1 year of follow-up. A total of 189 patients (92 males and 97 females; American Society of Anesthesiologists Physical Status I or II, Glasgow Coma Scale = 15) who were scheduled for laparoscopic abdominal surgery received intravenous midazolam (Versed®) 0.08-0.01 mg/kg and fentanyl (Duragesic®) 5.0 μg/kg. The main outcome measure was the degree of postoperative pain, as assessed using the Visual Analog Scale (VAS). VAS scores were recorded 5, 15, 30, 45, and 60 minutes after a fentanyl bolus injection in the post-anesthesia care unit (PACU). The minute expiratory volume, end-tidal carbon dioxide concentration (EtCO2) and respiratory rate (RR) were measured continuously. The incidence of fentanyl-induced respiratory depression (RR 45 mmHg) was recorded at its appearance and treated with respiratory assistance. Blood gas analysis was done 15, 30, 45, and 60 minutes after extubation. These parameters were correlated with genotyping results of genomic DNA extracted from whole blood. Results: Patients with the OPRM1 118 AG or GG genotypes had significantly higher VAS pain scores 15 and 30 minutes after a fentanyl bolus injection in the PACU than AA genotype patients (p G polymorphism lessens the analgesic response to fentanyl and the time to awakening and extubation but has no clinically significant effect on the incidence of respiratory depression.