Use of antibiotics for nongastrointestinal (non-GI) infections results in a three- to fivefold increase in the risk of inflammatory bowel disease (IBD) flare-ups, a study has found. The risk gradually declines and returns to baseline level about 6 weeks after exposure.
“This temporal pattern suggests that antibiotics may act as short-term triggers for IBD flare-up,” the investigators said. “We further demonstrated that oral formulations and broad-spectrum antibiotics were associated with a higher short-term incidence of IBD flare-up, whereas no such association was observed for injectable or narrow-spectrum antibiotics.”
This self-controlled case series study used territory-wide electronic medical records from Hong Kong, particularly from adults with IBD who had at least one flare-up and received at least one course of antibiotics for infections outside the GI tract between 2000 and 2024. The incidence rate ratios (IRRs) were estimated using conditional Poisson regression models.
A total of 810 patients were included in the analysis. The incidence of IBD flare-up was elevated during the month preceding antibiotic use (IRR, 2.85), further increasing during treatment (IRR, 3.44), and reached its peak within 2 weeks after treatment (IRR, 4.79). This returned to baseline levels within 6 months. [Am J Gastroenterol 2026;121:2280-2287]
Notably, the elevated incidences observed for oral antibiotics occurred during treatment (IRR, 3.91) and 2 weeks thereafter (IRR, 3.70), but not for injectable antibiotics (p<0.01 for interaction). Furthermore, broad-spectrum antibiotics demonstrated higher IRRs than narrow-spectrum agents from 1 month before to 6 weeks after exposure compared with baseline.
“Oral antibiotics were associated with a significantly increased risk of IBD flare during treatment and within 14 days after discontinuation, whereas no such trend was observed with injectable formulations,” the investigators said.
“Injectable antibiotics are typically reserved for more severe or systemic infections and may exert less direct impact on the gut microbiota, compared with oral agents, which pass through the GI tract and more directly disrupt the luminal microbial environment,” they added. [Gut 2016;65:1906-1915; ACS Infect Dis 2021;7:1283-1296]
Route and spectrum
An earlier study also found that oral antibiotics could promote antibiotic resistance among healthy commensal microbes to a greater extent than intravenous agents. [Antimicrob Agents Chemother 2013;57:3659-3666]
Moreover, broad-spectrum antibiotics exhibited a more profound effect on the risk of IBD flare than did narrow-spectrum agents. This was potentially driven by the former’s more extensive disruption of commensal microbial communities, resulting in greater dysbiosis. [Gut 2016;65:1906-1915]
“Given the frequent use of antibiotics in clinical practice among patients with IBD, our findings underscore the importance of balancing antimicrobial efficacy against potential short-term risks related to IBD flare-up, particularly during and 2 weeks after treatment,” the investigators said. “Close monitoring of disease activity in the short-term is advisable after antibiotic use.”
These findings also underscore the importance of caution in prescribing antibiotics, suggesting the use of agents with less impact on the gut microbiota, such as injectable formulations or narrow-spectrum antibiotics, according to the investigators.
“Importantly, our results do not apply to antibiotics prescribed for GI infections, such as Clostridioides difficile infections, which were not studied in our study,” they said. “These findings should not discourage the appropriate use of antibiotics when clearly indicated, but rather support careful selection of route and spectrum and short-term monitoring for disease activity in patients with IBD.”