Postoperative nausea and vomiting (PONV) is the major cause of patient's discomfort after surgery. Dexamethasone and ondansetron have been known to have some preventive effects on PONV. The purpose of this study was to compare the effects combination therapy of these drugs in the prevention of PONV after tympanomastoidectomy which has been known to be a high risk factor of PONV.

Ninty patients scheduled tympanomastoidectomy under general anesthesia were included. Patients were randomly divided into three groups and received dexamethasone 5 mg (group D), ondansetron 4 mg (group O), or dexamethasone 5 mg plus ondansetron 4 mg (group DO) at 30 min before the end of operation. The degree of PONV was assessed at 6 h, 12 h, 24 h, and 48 h after operation.

The degrees of nausea in group DO during 0-6 h and 6-12 h were lesser than those of other groups. The overall incidences of nausea were 73% (group D), 62% (group O), and 23% (group DO, P < 0.05). The degrees of vomiting in group O and DO during 0-6 h were lesser than those of group D. The overall incidences of vomiting were 37% (group D), 17% (group O), and 7% (group DO, P < 0.05).

The combination of dexamethasone and ondansetron is more effective than single use of each drug for the prevention on PONV after tympanomastoidectomy.