Prophylactic Effect of Ondansetron for Intrathecal Fentanyl-Induced Pruritus

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. 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 8mg 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, χ2, Fisher exact test, and Spearman linear correlation coefficient. 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). 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.