Rifaximin is a minimally absorbed oral antibiotic typically used to treat gastrointestinal (GI) disorders such as irritable bowel syndrome (IBS), small intestinal bacterial overgrowth (SIBO), and hepatic encephalopathy. Emerging evidence suggests that the gut microbiome plays a significant role in the pathogenesis of autism spectrum disorders (ASD), particularly in influencing gastrointestinal and behavioral symptoms. Hence, modifying gut flora with agents such as rifaximin is hypothesized to improve some ASD-related symptoms.

see cnke article Rifaximin in Autism Spectrum Disorder (ASD)