CDA and colitis: Also, antibacterial use leads to an increased risk of hematologic toxicity and gastrointestinal dose-limiting side effects of chemotherapy via the reduction of the isoform population of cytidine deaminase which is relevant to gemcitabine metabolism (CDD).20 Lastly, in patients with melanoma, the use of antibiotics increased the risk of colitis during immunotherapy.18 This could be due to the reduction of microbiome diversity and the high presence of pro-inflammatory bacteria following the use of antimicrobial drugs.18