The effect of intraperitoneal ondansetron on intrathecal bupivacaine analgesic activity in the thermal pain model or rats

Objective: The aim of this study is to investigate the effect of systemic (intraperitoneally) two different doses ondansteron administration on analgesic activity of bupivacaine administered intrathecally in rats. Material and Method: 24 rats were included in the study. Spinal catheters were placed to all subjects under anesthesia. Subjects were randomized to 4 groups: Group Saline (Group SF) (n=6) 10 ?L of saline was administered intrathecally (IT) and 0.5 mL of saline was administered intraperitoneally. Group Bupivacaine (Group B) (n=6) 10 ?L of bupivacaine was administered IT and 0.5 mL of saline was administered intraperitoneally. Group Bupivacaine Ondansetron1 (Group BO1) (n=6) 10 ?L of bupivacaine was administered IT and 0.5 mL 1 mg/kg ondansetron was administered intraperitoneally. Group Bupivacaine Ondansetron4 (Group BO4) (n=6) 10 ?L of bupivacaine was administered IT and 0.5 mL 4 mg/kg ondansetron was administered intraperitoneally. Catheter was flushed with 10 ?L of saline after drug administrations. Tail-flick test was applied to rats before and 5,10,20,30,45,60,90,120 minutes after intrathecal and intraperitoneal drug administrations. The presence of simultaneous motor block was evaluated with motor block evaluation scale. Mean values of the measurements were recorded. Data were showed as the percentage of maximum possible effect.(%MPE) Results: As a result of tail-flick test, mean tail-flick values of Group B were significantly higher at each time compared to Group SF (p<0.05). Mean tail-flick values of Group BO1 were significantly lower compared to Group B (p<0.05). Mean tail-flick values of Group BO4 were also significantly lower than mean tail-flick values of Group B. When mean tail-flick values of Group BO4 are compared to mean values of Group BO1, mean values of Group BO4 were significantly lower (p<0.05). As a result of motor block evaluation, no motor block was determined in any measurement minutes. Conclusion: This study showed that, the analgesic activity of 10 ?L of intrathecal bupivacaine was reduced by 1 mg/kg intraperitoneal ondansetron and this reduction was much more evident with 4 mg/kg intraperitoneal ondansetron. Keywords: Intrathecal bupivacaine, intraperitoneal, ondansetron, analgesia