The most commonly studied antibiotic for the treatment of bloating is rifaximin (77-79).Global symptomatic improvement in IBS patients treated with antibiotics has correlated withnormalization of hydrogen levels in lactulose hydrogen breath testing (77,80). This suggests thatthe rationale for using antibiotics is to modify the gut microbiome and reduce bacterialproduction of gas. Patients with non-constipation IBS randomized to rifaximin 550 mg TID for14 days had a greater proportion of relief of IBS-related bloating compared to placebo (79) for atleast 2 of the first 4 weeks after treatment (40.2% vs. 30.3%, p