Adverse events in analgesic

treatment with tramadol associated with CYP2D6 extensive-metaboliser and OPRM1 high-expression variants Tramadol, alone or in combination with paracetamol, is an effective analgesic that relieves the moderate to severe pain that accompanies various disorders (including osteoarthritis) and fol-lows surgical operations. However, this synthetic atypical opioid frequently evokes various adverse events (AEs), and the most frequent are nausea and vomiting.1 Although the mode of tram-adol-induced nausea/vomiting is unclear, opioid receptors on the chemoreceptor trigger zone in the human brain can bind opioids to cause nausea/vomiting.2 A major pathway of tramadol metab-olism is demethylation to O-desmethyltramadol by cytochrome P450 enzyme 2D6 (CYP2D6),3 and O-desmethyltramadol ha