Objective: To understand the effects of fluoxetine and paroxetine with ondansetron on the intestinal motility of rabbit ileum.
Study Design: Observational study.
Place and Duration of Study: The study was conducted from March to April 2018 in a multidisciplinary lab of Army Medical College, Rawalpindi.
Materials and Methods: The contractile effect of intestinal motility was recorded in the power lab. Subjects were twenty four healthy rabbits (Oryctolagus Cuniculus). Semi log dose-response curve was constructed for increasing concentrations of serotonin, ondansetron, fluoxetine, and paroxetine (10-9 to 10-6 M) alone and then in the presence of a fixed concentration of ondansetron (10-6 M) to observe the modulatory role of ondansetron. The serotonin mediated contractions were taken as control.
Results: Ondansetron and serotonin caused an increase in the contractile response of rabbits ileum. A depressive response was observed when the contractions were recorded with increased concentration of fluoxetine and paroxetine in the presence of ondansetron.
Conclusion: Ondansetron when used concomitantly with selective serotonin reuptake inhibitors(SSRIs), abolishes their antidepressant effects by causing a decrease in the intestinal motility of rabbit ileum.

Key Words: Chemotherapy-Induced Nausea and Vomiting, Ondansetron, Power Lab, Serotonin, SSRIs (selective serotonin reuptake inhibitors).