Methods of treating a bacterial lung infection are provided and comprise administering an effective amount of rifaximin to a subject in need thereof. The rifaximin can be delivered by inhalation therapy, such as by delivering the rifaximin in aerosol form. The rifaximin is administered alone or in combination with tobramycin, including in multiple doses. Methods of reducing biofilm formation are also provided and comprise contacting a bacteria with an effective amount of rifaximin. Pharmaceutical composition are also included and comprise rifaximin and a pharmaceutically-acceptable vehicle suitable for administering the rifaximin in aerosol form.