The effect of ondansetron on analgesic efficacy of acetaminophen after hysterectomy: A randomized double blinded placebo controlled trial

Abstract Objectives To determine that perioperative ondansetron reduces the analgesic efficacy of acetaminophen. Design Randomized, double-blinded study. Patients 120 patients ASA I-II who underwent abdominal hysterectomy. Interventions All the patients were given 1 g acetaminophen at skin closure. Patients were divided into two groups; ondansetron HCl (8 mg, 2 ml IV) (Group I, N = 60) and saline (2 ml IV) (Group II, N = 60) at the skin closure. Measurement Postoperative pain scores (VAS) while resting in bed and sitting, total opioid consumption were noted. Main results Patients randomized to ondansetron had significantly worse pain scores upon arrival to the recovery unit [by 1.7 (99.7% CI: 0.75, 2.59) cm] and at 1 h [by 1.3 (0.5, 2.1) cm] while resting in bed. Pain scores while sitting were also significantly greater in ondansetron group at arrival in PACU by 0.6 (99.7% CI: 0.1, 1.0) cm. Thereafter, pain scores did not differ significantly. Median total opioid (tramadol) consumption was 441 [Q1, Q3: 280, 578] mg in the ondansetron group and 412 [309, 574] mg in the placebo group, P = 0.95. Conclusions Ondansetron significantly decreased the analgesic effect of acetaminophen during the initial postoperative period. Our results thus confirm that acetaminophen analgesia is partially mediated by serotonin receptors. However, the reduction was of marginal clinical importance and short-lived.