Analysing the effect of the nonsteroidal anti-inflammatory drug ketorolac on the composition of small intestinal microbiota and bile acids Although the influence of NSAIDs on the composition of intestinal microbiota is well established, the underlying mechanism is still poorly understood. Intestinal injury and mucosal inflammation caused by NSAIDs is likely to be a major factor driving the changes of microbiota. Also the direct antibacterial properties of some NSAIDs, or their effect on intestinal motility may contribute to dysbiosis. Our present analysis demonstrates that ketorolac given at low, non-damaging dose for 4 weeks caused small intestinal dysbiosis, and these changes were accompanied by and correlated with significant bile acid alterations. GI transit was not influenced significantly by ketorolac. These results suggest that besides direct effects on bacteria, intestinal inflammation and stasis also other, yet unidentied, factors may contribute to NSAID-induced dysbiosis and bile dysmetabolism.