Efficacy of mirtazapine in preventing intrathecal morphine-induced nausea and vomiting after orthopaedic surgery*.

Nausea and vomiting are frequent complications of intrathecal morphine. In this randomised, double-blind trial, we tested the efficacy of mirtazapine, an antidepressant that blocks receptors associated with vomiting, on the incidence of nausea and vomiting after intrathecal morphine. One hundred patients receiving spinal anaesthesia for lower limb surgery were assigned equally to take either an orally disintegrating form of 30 mg mirtazapine or matching placebo 1 h before surgery. Spinal anaesthesia was performed by injection of 15 mg isobaric bupivacaine 0.5% along with 0.2 mg preservative-free morphine. Nausea and vomiting were evaluated 3, 6, 12, 18 and 24 h after intrathecal morphine administration. The incidence of nausea and vomiting was significantly lower in patients receiving mirtazapine compared with placebo (26.5% vs 56.3%, respectively; p = 0.005). The mean (SD) onset time of postoperative nausea and vomiting was significantly delayed in mirtazapine patients: 9.4 (2.5) vs 5.2 (1.8) h, respectively; p < 0.0001. The severity of nausea and vomiting was also decreased after mirtazapine at the 3-6 h and 6-12 h periods. Our data indicate that pre-operative mirtazapine decreases the incidence, delays the onset and reduces the severity of nausea and vomiting induced by intrathecal morphine in patients undergoing spinal anaesthesia.