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 micro g] 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, chi[2], 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 T[6] dermatomes and 74% of patients with pruritus in case group had pruritus in T[6]-L[1] dermatomes. The incidence of pruritus in L[1]-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 T[6]-L[1] dermatomes. Ondansetron injection does not influence systolic blood pressure, duration of anesthesia and analgesia, and does not induced urinary retention and back pain