Antibiotic Use for Cystitis and Risk of Treatment Failure in Pregnancy Following Gastric Bypass: A Cohort Study

Cystitis is common during pregnancy and requires effective antibiotic treatment to prevent complications. Gastric bypass surgery alters gastrointestinal anatomy and may impair oral drug absorption, raising concerns about antibiotic effectiveness. We therefore aimed to examine antibiotic use for cystitis and the risk of treatment failure in pregnant women with prior gastric bypass. In this nationwide Danish register-based study, we compared 1985 pregnancies among women with prior gastric bypass with 1 400 174 pregnancies among women without bariatric surgery. We assessed redeemed prescriptions for cystitis-related antibiotics and potential treatment failure defined as repeated antibiotic prescriptions within 14 days, hospital-recorded cystitis or severe urinary tract complications (pyelonephritis or urosepsis). Pregnant women with prior gastric bypass more frequently redeemed cystitis-related antibiotics than those without bariatric surgery (22.6% vs. 12.7%). Among antibiotic-exposed pregnancies, prior gastric bypass was associated with an increased risk of potential treatment failure, including repeated antibiotic prescriptions (adjusted odds ratio [aOR] 1.69, 95% confidence interval [CI] 1.22-2.30) and hospital-recorded cystitis (aOR 2.22, 95% CI 1.24-3.67), while severe complications were rare. These findings suggest that antibiotic treatment may be less effective or that the clinical course is more complicated in this group, highlighting a need for closer monitoring and tailored treatment strategies.