A man in his mid-40s with known auto-brewery syndrome (ABS) was brought to an emergency department in Switzerland in early 2025 after being found unresponsive at home. He had started amoxicillin/clavulanate 5 days earlier for community-acquired pneumonia, following approximately 2 years without ABS symptoms.
At presentation, the patient had a Glasgow Coma Scale score of 9 and a blood alcohol concentration of 43.6 mmol/L despite reported abstinence, which his partner confirmed. Arterial blood gas results were within normal limits, and cranial computed tomography showed no intracranial hemorrhage or structural brain damage. Empiric naloxone and flumazenil produced no clinical improvement. The findings were consistent with recurrent endogenous ethanol intoxication following antibiotic exposure.
The patient received supportive care in the intensive care unit, and amoxicillin/clavulanate was discontinued. He remained afebrile, and inflammatory markers were within normal limits. Following rehydration, he recovered within hours and was discharged with a Glasgow Coma Scale score of 15 and no neurologic deficits. The clinical team concluded that he had experienced endogenous ethanol intoxication from ABS, likely exacerbated by antibiotic-induced dysbiosis following the recent antibiotic treatment.
The patient's earlier clinical course provided additional context for the diagnosis. His history included alcohol misuse in 2020, followed by episodes of elevated blood alcohol concentrations despite reported abstinence. Approximately 2 months following inpatient psychiatric rehabilitation for alcohol misuse in 2020, he was hospitalized despite reported abstinence with a blood alcohol concentration of 46.8 mmol/L. He subsequently experienced recurrent alcohol odor despite abstinence, and home breathalyzer testing consistently showed elevated levels. Gastroenterologic evaluation in 2023 identified small intestinal bacterial overgrowth and increased Proteobacteria, predominantly Enterobacter species, whereas Klebsiella species were not detected. Treatment with a 14-day course of rifaximin and probiotics was followed by an approximately 2-year asymptomatic period.
The investigators proposed that disruption of the gastrointestinal microbiome following antibiotic treatment may have contributed to the recurrence. Although ABS has been associated with ethanol-producing yeast species, they noted growing evidence that bacteria may also contribute to endogenous ethanol production. The investigators cited previous case reports in which antibiotic exposure preceded symptoms in 7 of 16 ABS cases, supporting a possible relationship between microbial imbalance and ABS recurrence.
The findings were limited by the single-patient case design and could not establish that amoxicillin/clavulanate caused the recurrence. The proposed role of antibiotic-induced dysbiosis was a clinical hypothesis based on the temporal association and the patient's history. Interpretation was further complicated by previous alcohol overuse, small intestinal bacterial overgrowth, altered gut microbiota, and ABS episodes that preceded the recent antibiotic exposure.
The authors concluded that ABS should be considered in cases of otherwise unexplained alcohol intoxication when reported abstinence is credible and suggested caution with antibiotic therapy in patients with known ABS. “In patients with known ABS, antibiotic therapy should be approached with caution, considering possible relapse of the disease,” wrote lead study author Philipp Widmer, of the Department of Internal Medicine at Luzerner Kantonsspital in Switzerland, and colleagues.
The authors reported no conflicts of interest or funding.
Source: Oxford Medical Case Reports
