Does methylnaltrexone reduce the incidence and severity of itch following spinal anaesthesia with intrathecal morphine in women undergoing caesarean delivery.

INTERVENTION: The study drug will be 12 mg methylnaltrexone (MNTX) in 0.6 ml solution for subcutaneous injection into the anaesthetised anterolateral thigh at the completion of surgery. CONDITION: Incidence and severity of pruritus after intrathecal morphine at caesarean delivery PRIMARY OUTCOME: The severity of intrathecal morphine‐induced pruritus among woman delivering by elective caesarean section under spinal anaesthesia, as determined by the mean maximum pruritus score in the first 24 hours after surgery and the 0‐24 hour area under the curve for pruritus scores. Pruritus will be scored on a 0‐10 verbal numerical rating scale = VNRS SECONDARY OUTCOME: The OBAS (overall benefit of analgesia score). The incidence of cramping abdominal pain in the first 24 hours after delivery by elective caesarean section under spinal anaesthesia. Presence and severity (VNRS 0‐10) of gastrointestinal cramps. The incidence of intrathecal morphine‐induced pruritus in the first 24 hours postoperatively, among women delivering by elective caesarean section under spinal anaesthesia. VNRS score >0. The incidence of intrathecal morphine‐induced pruritus requiring treatment in the first 24 hours postoperatively among women delivering by elective caesarean section under spinal anaesthesia. The incidence of nausea and/or vomiting in the first 24 hours after delivery by elective caesarean section under spinal anaesthesia. VNRS>0. INCLUSION CRITERIA: 1. American Society of Anesthesiologists classification 1 or 2 2. Elective caesarean section under spinal anaesthesia, with or without epidural catheterization