Mu opioid receptor encoded by OPRM1 is crucial for the analgesic effect of opioid drugs. It is the target of tramadol, a centrally acting opioid analgesic for the treatment of moderate to severe acute and chronic pain. Genetic polymorphisms of the OPRM1 and miRNA genes may affect the outcome of tramadol treatment due to altered expression or receptor sensitivity. The aim of this study was to determine the frequencies of OPRM1 rs1799971, OPRM1 rs677830, MIR23B 1011784 and MIR107 rs2296616 polymorphisms in the group of patients after breast cancer surgery. Genotyping with quantitative allele-specific polymerase chain reaction was performed to evaluate the impact of these polymorphisms on the severity of acute pain and the presence of adverse effects, chronic and neuropathic pain. Carriers of at least one polymorphic MIR107 rs2296616 A allele had a lower risk of nausea in the third week of treatment, and patients with MIR23B 1011784 GG genotype had a higher risk of nausea in the fourth week. A higher risk of constipation during the first month was confirmed in carriers of at least one polymorphic OPRM1 rs1799971 G allele and in the third week in carriers of at least one polymorphic OPRM1 rs677830 T allele. The presence of MIR107 rs2296616 polymorphism increased the risk of chronic pain, the presence of MIR23B 1011784 polymorphism increased the risk of neuropathic pain, and the presence of the OPRM1 rs677830 polymorphism reduced the risk of neuropathic pain. The effect of the polymorphisms on the intensity of acute pain has not been confirmed.
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