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.

Patients 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, χ2, 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).

Conclusions: 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.