Pruritus after intrathecal morphine for cesarean delivery: incidence, severity and its relation to serum serotonin level

•Intrathecal morphine-induced pruritus is common in parturients.•The exact mechanism of intrathecal morphine-induced pruritus is unclear.•Interaction between morphine and 5-hydroxytryptamine receptors may have a role.•Serum serotonin levels increased significantly after intrathecal morphine.•Serotonin may have a role in the genesis of intrathecal morphine-induced pruritus. Pruritus is the most common side effect of intrathecal morphine, especially in parturients. The exact mechanism is not clear and many possible mechanisms have been suggested. Among these is the activation of the 5-hydroxytryptamine sub-type-3 receptors by intrathecal morphine. Forty parturients who underwent elective cesarean delivery under spinal anesthesia were divided into two groups of 20 each in this prospective, randomized study. Both groups received an intrathecal injection of 0.5% (2–3 mL) hyperbaric bupivacaine in addition to 100 μg of morphine in group 1 (M100) and 200 μg of morphine in group 2 (M200). Two blood samples were taken from each patient for serotonin estimation, preoperatively and four hours later. Postoperatively, all patients were assessed for pruritus (incidence and severity), pain (visual analog pain scale), first request for analgesia, and total analgesic dose required within 24 hours. The serum serotonin level increased significantly postoperatively, by 283% versus 556% (P