Antibiotics increase inflammatory bowel disease (IBD) risk, according to researchers who used Danish data to capture 36,017 new cases of ulcerative colitis (UC) and 16,881 new cases of Crohn’s disease (CD).

The researchers followed 6.1 million people aged 10 years and older for approximately 87.1 million person-years. Compared with controls who did not receive antibiotics, antibiotic users were more likely to develop UC and CD: by 21 and 40 per cent respectively in those aged 10-40 years; by 44 and 62 per cent at 40-60 years; and by 47 and 51 per cent in people aged 60 years and older.

Each antibiotic course increased IBD risk by 11 per cent in those aged 10-40 years; by 15 per cent at 40-60 years of age; and by 14 per cent in people 60 years and older. IBD risk approximately doubled after five or more antibiotic courses: by 69 per cent in those aged 10-40 years; by 112 per cent at 40-60 years; and by 95 per cent at 60-plus years.

IBD risk peaked one to two years after taking antibiotics. People aged 10-40 years were 40 per cent more likely to develop IBD one to two years after taking antibiotics compared with 13 per cent four to five years after exposure. The risks were 66 and 21 per cent respectively at 40-60 years of age, and 63 and 22 per cent in people 60 years and older.

IBD risk was highest with nitroimidazoles (31-61 per cent depending on age) and fluoroquinolones (54-76 per cent), which are used commonly against gastrointestinal pathogens. Nevertheless, antibiotics less commonly used against gastrointestinal pathogens (such as narrow-spectrum penicillins) also increased IBD risk. Nitrofurantoin, which has limited effect on gastrointestinal flora, was not associated with IBD risk.

The findings support the notion that “alterations in the gut microbial environment may play a significant role in the development of IBD, and highlights the important point that many antibiotics, including those not used to treat gastrointestinal pathogens, can affect the intestinal microflora”. (Gut doi:10.1136/gutjnl-2022-327845 1)