Ondansetron Does Not Attenuate the Analgesic Efficacy of Nefopam

Objectives: The aim of this study was to investigate if there is any interaction between ondansetron and nefopam when they are continuously co-administrated during patient-controlled intravenous analgesia (PCIA). Methods: The study was a prospective, randomized, controlled, non-inferiority clinical trial comparing nefopam-plus-ondansetron to nefopam alone. A total of 230 postoperative patients using nefopam for PCIA, were randomly assigned either to a group receiving continuous infusion of ondansetron (Group O) or to the other group receiving the same volume of normal saline continuously (Group N). Postoperative pain intensity scores, the sum of pain intensity difference over 24 hours postoperatively (SPID(24hr)), the incidence of adverse events, and the total consumption of nefopam were evaluated respectively. Results: Postoperative pain was treated successfully in both groups. The mean SPID(24hr) scores were 95.6 mm in Group N and 109.3mm in Group O [95% confidence interval (CI) -14.28, 24.32]. The lower margin of the 95% CI was above the pre-determined non-inferiority margin (-30mm) for SPID(24hr), which indicated that nefopam-plus-ondansetron was not worse than the nefopam alone in term of analgesic efficacy. In addition, there was no statistical difference between the two groups in term of cumulative consumption of nefopam. Compared with Group N, postoperative vomiting was significantly reduced in Group O during the postoperative 24 hours (P < 0.05). Less rescue antiemetics were given to patients in Group O than those receiving nefopam alone (P < 0.05). There were no differences in postoperative nausea between the two groups. Conclusion: Nefopam-plus-ondansetron is not inferior to nefopam alone in relieving the pain in PCIA after minimally invasive surgery. In addition, adverse events are reduced without compromising analgesic efficacy.