Oral antibiotics and risk of new colorectal adenomas during surveillance follow-up

Background: Antibiotics may increase colorectal neoplasia risk by modifying the gut microbiome. It is unknown whether use is associated with the risk of new colorectal adenomas among individuals with prior adenomas. Methods: We performed a secondary analysis of four randomized clinical trials for the chemoprevention of colorectal adenomas. Participants self-reported all currently used prescription drugs shortly after an initial colorectal adenoma diagnosis and two or three times a year thereafter over 3 to 5 years of follow-up. We estimated adjusted risk ratios (RR) with 95% confidence intervals (CI) for incident adenomas, analyzing the four trials together. Results: Cumulatively, the four trials enrolled 5,174 participants (3,491 men and 1,683 women), of whom 4,769 (92%) completed ≥1 follow-up colonoscopy. A total of 763 (15%) participants reported using oral antibiotics on ≥2 occasions. Overall, 39% of those using oral antibiotics at least twice developed new colorectal adenomas compared with 40% of those with no use or a single report of use (RR, 0.99; 95% CI, 0.90–1.10). No statistically significant associations were found in study-specific analyses, and results were similar for high- and low-risk adenoma findings, antibiotic class, anatomic location of adenomas, and analyses excluding those with interim colorectal exams. Conclusions: Oral antibiotic use during colonoscopic surveillance after an initial adenoma diagnosis was not associated with risk of these polyps. Impact: Any changes to the gut microbiome as a consequence of oral antibiotic use during surveillance may not affect the development of metachronous colorectal adenomas.