Randomized, double-blind, placebo-controlled study to investigate the pharmacodynamic interaction of 5-HT3 antagonist ondansetron and paracetamol in postoperative patients operated in an ENT department under local anesthesia.

BACKGROUND: The preclinical incision pain models and clinical studies in healthy volunteers have demonstrated the central serotonergic analgesic mechanism, paracetamol analgesia. This has been evidenced by raised serotonin concentrations in the brain following paracetamol administration in a few studies. The inhibition of paracetamol analgesia by 5-HT3 antagonists suggests that this analgesia is 5-HT3 mediated. However, in a few studies, 5-HT3 antagonists themselves exhibited an analgesic action. Various studies in this context stated intricate results. The present study was intended to understand the pharmacodynamic interaction between paracetamol and ondansetron in postoperative patients.

METHODS: This randomized clinical trial included 32 postoperative cases of either sex, ages between 18 and 70 years. The patients were randomly allocated into the placebo and test groups and received respective treatment at the end of surgery. The pain score was recorded using Visual Analogue Scale (VAS) and Face, Legs, Activity, Cry, Consolability (FLACC) behavioral scale at awakening and every 30 min for the next 3 h. The postoperative rescue analgesic consumption for 24 h was recorded. The data were analyzed using OpenEpi and SciStatCalc statistical software.

RESULTS: A significantly higher pain score was observed in the placebo group postoperatively for 60 min on VAS (p<0.05 and p<0.01), whereas the FLACC behavior scale score was significantly higher at 120 and 150 min (p<0.05). The test group patients were more comfortable throughout the study, and the postoperative analgesic requirement was significantly lesser (p<0.05).

CONCLUSIONS: The pharmacodynamic interaction between paracetamol and ondansetron coadministration does not block but instead increase paracetamol analgesia, reduce the postoperative analgesic requirement, and improve the postoperative comfort level.