Prophylactic Effect of Ondansetron for Intrathecal Fentanyl-Induced Pruritus

Background: using opioids along with local analgesic increase anesthesia duration and provide appropriate postoperative analgesia. however, intrathecal injection of opioids is associated with upsetting side effects including pruritus. ondansetron (5-ht3 receptor agonist) has anti-pruritus effects. therefore, we conducted a double blind randomized case-control study to evaluate prophylactic effects of ondansetron for preventing intrathecal fentanyl-induced pruritus.materials and methods: two hundred seven patients with asa status i, ii or iii, who were candidate for pelvic or lower extremity surgery with spinal anesthesia (sa) using bupivacaine hyperbaric (10-15 mg) and fentanyl (25 µg) were included in the study. patients were randomly assigned to two groups of case (ondansetron 8 mg iv) and control (4 ml normal saline iv). patients’ hemodynamic indexes and side effects were evaluated at 5, 10, 30, 60 minutes and then hourly up to 6 hours after sa. pruritus presence, degree, and site were evaluated after two and six hours. data were analyzed using kolmogorov-smirnov test, student t-test, mann–whitney u, ?2, fisher exact test, and spearman linear correlation coefficient.results: the pruritus incidence was 60% in control and 34% in case group. severe pruritus was observed in 18% of control group and 6% of case group. ninety four percent of patients with pruritus in control group expressed it in above t6 dermatomes and 74% of patients with pruritus in case group had pruritus in t6-l1 dermatomes. the incidence of pruritus in l1-lower dermatomes was similar in two groups. headache and nausea after anesthesia were more common in control group (p=0.035).conclusion: ondansetron decrease incidence and degree of intrathecal fentanyl-induced pruritus. this reduction was more significant around injection area t6-l1 dermatomes. ondansetron injection does not influence systolic blood pressure, duration of anesthesia and analgesia, and does not induced urinary retention and back pain.