Disclosed herein are methods of treating a patient having an intestinal disorder, the methods comprising: administering to a patient in need thereof a pharmaceutical composition comprising a hydrate or solvate form of rifaximin in polymorphic form &bgr;, alone or in a mixture with other crystalline, hydrate, solvate or amorphous forms of rifaximin, in gastroresistant microgranules, wherein the rifaximin is administered at a dose of at least 800 mg per day for a period of at least 7 days.