Indication for the treatment of patients (over 12 years of age) with travelers diarrhea caused by noninvasive strains of escherichia coli. rifaximin is also designated an orphan drug by the food and drug administration for the adjunctive treatment of hepatic encephalopathy to reduce blood ammonia concentrations and decrease severity of neurological manifestations.mechanism of action rifaximin acts by inhibiting rna synthesis in susceptible bacteria by binding to the beta-subunit of bacterial deoxyribonucleic acid (dna)-dependent ribonucleic acid (rna) polymerase enzyme. this results in the blockage of the translocation step that normally follows the formation of the first phosphodiester bond, which occurs in the transcription process.