This study aims to determine which of 3 doses of a non-absorbable antibiotic Rifaximin is most effective in treating active moderate Crohn's disease. Rifaximin tablets are already marketed in some European countries and the USA to treat traveller's diarrhoea. A new gastro-resistant form of Rifaximin called Rifaximin-Extended Intestinal Release (EIR) will be used in this study. These tablets dissolve in the stomach,releasing gastro-resistant granules which pass into the intestines and deliver Rifaximin directly to the site of the disease. Rifaximin is not absorbed, making it more effective and greatly reducing the frequency of side effects.

Inclusion Criteria:

• diagnosis of Crohn's disease localised in the ileum and/or colon, documented either radiologically or endoscopically at least 3 months previously;
• patients with a CDAI of ≥ 220 to ≤ 400;
• patients capable of and willing to conform to the study protocol;
• patients who have provided signed and dated written informed consent.

Exclusion Criteria:

• patients potentially needing immediate surgery for Crohn's disease, including patients with occlusive symptoms and/or stenotic tract with dilation above;
• patients with active perianal Crohn's disease;
• patients with other infectious, ischemic, or immunological diseases with gastrointestinal involvement;
• patients with symptoms attributed to Short Bowel Syndrome or previous surgery;
• patients with stoma;
• patients affected by upper gastro-intestinal disease (gastro-duodenum-jejunum Crohn's disease) alone or in combination with colitis or ileitis;
• patients treated with: oral steroids and budesonide less than 30 days prior to screening; i.v. steroids less than 30 days prior to screening; antibiotics (such as metronidazole, tinidazole, ciprofloxacin, clarithromycin) less than 15 days prior to screening;
• rectal steroids less than 30 days prior to the screening visit;
• anti-tumour necrosis factor (anti-TNF) and other biological therapies less than 6 months prior to the screening visit;
• pregnant women or nursing mothers;
• females of childbearing age (unless surgically sterile) without a negative urine pregnancy test at screening and at enrolment;
• patients with severe hepatic insufficiency (Child C);
• patients with severe cardiac insufficiency (NYHA - New York Heart Association classes 3 - 4);
• patients with known hypersensitivity to Rifaximin;
• any condition or circumstance that would prevent completion of the study or interfere with analysis of study results, including a history of drug or alcohol abuse, mental illness or non-compliance with treatments or visits, with immunological (including HIV infection), haematological or neoplastic disease;
• withdrawal of informed consent;
• patients who have used any investigational drug (except biological therapies) within 3 months prior to screening;
• patients who have donated 250 ml or more of blood in the last 3 months.