Antiemetic efficacy of metoclopramide and diphenhydramine added to patient-controlled morphine analgesia: a randomised controlled trial

BACKGROUND AND OBJECTIVE: the objective of this study was to assess whether antiemetic drugs metoclopramide and diphenhydramine, administered together as opposed to alone, can have better efficacy in preventing postoperative nausea and vomiting when added to patient-controlled morphine analgesia. PATIENTS AND METHODS: during the period July 2007 to August 2008, 200 women scheduled for abdominal total hysterectomy were randomised to one of four postoperative, patient-controlled analgesia regimens: group 1, morphine 1 mg ml; group 2, morphine 1 mg ml with metoclopramide 0.5 mg ml; group 3, morphine 1 mg ml with diphenhydramine 0.6 mg ml; and group 4, morphine 1 mg ml with metoclopramide 0.5 mg ml and diphenhydramine 0.6 mg ml. Dexamethasone 4 mg was administered to all patients in all groups after anaesthesia induction as a prophylactic antiemetic medication, and prochlorperazine 5 mg was administered by intramuscular injection as necessary as a salvage/rescue therapy. Nausea, vomiting, pruritus, level of sedation, pain and morphine consumption were compared between the four groups. RESULTS: the incidence of nausea was significantly (P < 0.05) lower in group 4 compared to the other groups. In addition, there was a significant (P = 0.006) difference in the incidence of vomiting between groups 1 and 4. Repeated measurement analysis showed that numeric rating scale scores for group 4 were significantly (P < 0.001) lower than those for the other groups. CONCLUSION: results of this study showed that a combination of metoclopramide with diphenhydramine in patients treated with dexamethasone at anaesthesia induction decreased postoperative nausea and vomiting compared to metoclopramide or diphenhydramine in these patients, when added to patient-controlled anaesthesia with morphine.