Provided for in the instant application are two additional polymorphic forms of rifaximin namely substantially pure APO-I and APO-II. Also provided are processes for preparing substantially pure APO-I and APO-II. Rifaximin is a non-aminoglycoside antibiotic that has previously been found to be useful for the treatment of travellers diarrhea caused by Escherichia coli bacteria, as well as in the treatment of irritable bowel syndrome, diverticular disease, hepatic encephalopathy, pyogenic skin infections and as an antibacterial prophylactic prior to colon surgery.
