Second-line therapy for Helicobacter pylori eradication causing antibiotic-associated hemorrhagic colitis

OBJECTIVE: Helicobacter pylori (H. pylori) eradication rarely develops into antibiotic-associated hemorrhagic colitis (AAHC), in which the etiology of colitis remains unclear. We herein report a rare case of AAHC caused by second-line therapy for H. pylori eradication. RESULTS: A 65-year-old female was administered second-line therapy for H. pylori composed of 1500 mg of amoxicillin, 500 mg of metronidazole and 40 mg of vonoprazan for 7 days because of first-line therapy failure. A day after completing second-line therapy, she complained of abdominal pain and hematochezia. Colonoscopy revealed a hemorrhage and edematous mucosa with no transparent vascular pattern in the transverse colon. A bacterial culture detected Klebsiella oxytoca (K. oxytoca), but no other pathogenic bacteria. A drug-induced lymphocyte stimulation test (DLST) showed positive reactions for both amoxicillin and metronidazole. According to these findings, the patient was diagnosed with AAHC. Bowel rest for 6 days relieved her abdominal pain and hematochezia. CONCLUSIONS: The present case developed AAHC caused by second-line therapy for H. pylori eradication. The pathogenesis is considered to be associated with microbial substitution as well as a delayed-type allergy to antibiotics, suggesting that AAHC is a potential adverse event of second-line therapy for H. pylori eradication.