Intrathecal fentanyl-induced pruritus during labour: the effect of prophylactic ondansetron

Fentanyl is commonly used for spinal analgesia during labour but it is associated with a high incidence of pruritus. This randomised, double-blind, placebo-controlled study was performed to evaluate the effect of prophylactic ondansetron on the incidence and severity of pruritus among parturients receiving intrathecal fentanyl as part of combined spinal-epidural analgesia. Seventy-three women were randomised to receive either saline placebo (group P, n = 25), ondansetron 4 mg (group O4, n = 23) or ondansetron 8 mg (group O8, n = 25) intravenously before intrathecal fentanyl 25 micrograms and bupivacaine 2 mg. The incidence and severity of pruritus were measured using a verbal rating and a visual analogue scale, and by the requirement for rescue anti-pruritic medication (naloxone). The overall incidence of pruritus was 95% (group P 100%, group O4 95%, group O8 90%). There were no significant differences between groups for severity of pruritus or requirement for treatment (naloxone given to 45%, 28% and 35% of groups P, O4 and O8 respectively). Secondary outcomes such as the incidence of headache, pain and nausea were not significantly different between groups. We conclude that prophylactic ondansetron 4 or 8 mg intravenously was ineffective in reducing the incidence or severity of intrathecal fentanyl-induced pruritus during labour.