Effect of ondansetron on the analgesic efficacy of tramadol used for postoperative analgesia: a randomised controlled study

Abstract

Background: Ondansetron is used to reduce tramadol induced postoperative nausea and vomiting  (PONV). Studies on patient-controlled analgesia (PCA) found that ondansetron reduces the analgesic  efficacy of tramadol. Drug requirement in PCA and in conventional intravenous analgesia without PCA  device may differ. This study evaluated the effect of ondansetron on analgesic efficacy of tramadol for postoperative analgesia without a PCA device.
Methods: A prospective, randomised, placebo-controlled, double-blind parallel group study was  conducted on 126 euthyroid patients of ASA I and II, aged between 30 and 65 years undergoing  hemithyroidectomy under general anaesthesia. Patients were divided into group O and group C. At the time of closure of strap muscles, patients in group O received tramadol 1.5 mg/kg IV and ondansetron 0.1 mg/kg (diluted to 4 ml) IV and those in group C received tramadol 1.5 mg/kg IV and normal saline 4 ml IV. Duration of analgesia, pain score (VAS), PONV and sedation scores were analysed.
Results: Duration of analgesia was longer in group C compared with group O (164.1 min vs. 76.3 min, p < 0.05). Postoperative VAS score was higher in group O (p < 0.001). Group C showed higher PONV and sedation score.
Conclusion: Ondansetron reduces the duration and quality of analgesia of tramadol administered  conventionally without a PCA device.

Keywords: ondansetron, pain, postoperative nausea and vomiting, sedation, tramadol