Background: Propofol has widely used as an anesthetic induction and maintenance agent. Sixty percent of patients experienced pain on propofol injection. There were evidences that both dexamethasone and ondansetron can reduce propofol injection  pain. But the effectiveness of each drug is inconclusive when compare to lidocaine. We hypothesized that combination of dexamethasone and ondansetron is non-inferiority to lidocaine for reducing propofol injection pain.

Materials: 178 adult patients, ASA physical status I-III, undergoing elective surgery were randomly assigned to two groups. Group L received 2 mL of 2% preservative free lidocaine, group DO received dexamethasone 10 mg and follow by ondansetron 4 mg intravenously, 1 minute prior to 0.3 mg.kg-1 of propofol injection. Pain score, facial grimacing, vocalization and hand withdrawal were recorded 10 seconds after propofol injection.

Results: Overall incidences of propofol injection pain after pretreatment (34.83% versus 42.69% in group L and group DO, respectively, p = 0.26) and moderate to severe pain (11.24%  versus 12.36%  in  group  L  and  group  DO,  respectively,  p  =  0.81)  were  not  different  between the two groups. In order to prove the non-inferiority of dexamethasone and  ondansetron combination  against  lidocaine, the upper limit of the 90% confidence interval must be lower than the predefined margin of non-inferiority (3%). The upper limit of the incidence of moderate to severe pain was 2.99% which was lower than the predefined 3%.

Conclusion: Combination of dexamethasone 10 mg and ondansetron 4 mg was comparable to lidocaine 40 mg for pretreatment on propofol injection pain.