Background: The minimal effective analgesic concentration of opioids required for satisfactory analgesia may differ significantly among the patients. Genetic factors may contribute to the variable response to opioids by affecting their pharmacokinetics or pharmacodynamics. Methods: Ninety nine patients undergoing abdominal surgery with colorectal anastomosis because of colorectal carcinoma were enrolled in the present study. C34535T was genotyped in all subjects and the patients were divided

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... o three groups according to their genotype: CC-wild type homozygous, CT-mutant heterozygous and TT-mutant homozygous. Intravenous fentanyl, patient controlled analgesia was provided postoperatively for pain control in the first 24 hour after surgery. Opioid consumption, pain scores and the adverse side effects were evaluated. Results: Our main result is that the patients in the CC genotype group consumed significantly more fentanyl (375.0 μg ± 43.1) than the patients in the TT group (295.0 μg ± 49.1) and the CT (356.4 μg ± 41.8) group in the treatment of postoperative pain. The patients in the TT group had lower VAS scores at 6h, 12h, 18 h and 24h postoperatively. There were no significant differences in the side effects among the three groups regarding the vomiting and the sedation score. The patients in the TT group had more frequently nausea score 1, than the patients in the other two groups. Conclusion: Our study indicates that the C3435T SNPs of the ABCB1 gene is associated with differences in the opioid sensitivity. The ABCB1 polymorphism may serve as an important genetic predictor to guide the acute pain therapy in postoperative patients.