IntroductionControlled trials in children and adolescents have shown that, small-dose naloxone infusions (0.25µg/kg/hour) can significantly reduce opioid induced side effects without affecting opioid-induced analgesia. Material and methods84 elective thoracotomy patients having combined thoracic epidural and general anesthesia for thoracotomy surgeries were randomly assigned to one of the two study groups. All patients of Group A (n=42) received continuous intravenous infusion of naloxone at a calculated dose of 0.25µgkg -1 hr -1 and patients of Group B (n=42) received continuous intravenous infusion of normal saline at a fixed rate. All patients were premedicated with fentanyl 1 µg/kg i.v. After placement of epidural catheter at T 6-8 interspaces, all patients were administered morphine 0.1mg/kg with 0.125% bupivacaine immediately before induction of general anaesthesia. VAS was assessed immediately after extubation and a bolus dose of 0.01mg/kg epidural morphine was administered when VAS exceeded 3 in postoperative follow up period of 72hrs in all patients. We measured the incidence of side effects like vomiting, nausea, pruritus and respiratory depression and number of times rescue analgesic was required. ResultsSmall dose naloxone infusion significantly reduced the opioid induced side effects without antagonizing opioid induced analgesia. ConclusionNaloxone reduces epidural morphine-induced side effects without significant alteration of its analgesic effects.