Safety and Efficacy of AST-120 in Mild to Moderate Crohn's Patients With Fistulas

The experimental drug AST-120 is composed of black, odorless spherical carbon particles in 2g sachets (aluminum foil pouches). The placebo consists of microcrystalline cellulose spheres, Celphere CP-305, stained to match the appearance of AST-120, in 2g sachets (aluminum foil pouches). Both AST-120 and placebo are oral (taken by mouth)preparations. Both are tasteless. To take the product, patients will tear open the sachets, drop the contents directly on their tongue and wash it down with 8 ounces of water. Patients will be randomly assigned (like the toss of a coin), to receive either AST-120 or placebo. Patients will have a 50/50 chance of receiving placebo. Patients who participate in this study will be required to take a single dose of study drug (AST-120 or placebo) 3 times a day, 30 minutes after a meal, for 8 weeks, and be evaluated at Week 4 and Week 8. This is a 'blinded' treatment, which means that neither the patient nor the study doctor will know if the patient has received study drug or placebo. If, at the end of the first full course of randomized treatment, (8 weeks), patients are not showing an improvement in their condition, they may have the option to receive the alternate blinded treatment for one treatment course (8 weeks). The study doctor will discuss this option with each patient individually. During this second course of treatment, patients will be evaluated at Week 12 and Week 16. If the patient does not respond to the alternate blinded treatment, or their condition worsens after 4 weeks (assessed at Week 12), they may be removed from the study at the discretion of the investigator. If patients respond to either the initial treatment or the alternate blinded treatment, they will have monthly doctor/clinic visits for up to 6 months (Week 24), or until their condition worsens or they relapse. Patients will not receive any study drug during this follow-up period. Relapse is defined for this study as: * an increase by 1 or more in the number of draining fistulas for 2 sequential visits versus the number present at the time of response (response is defined as at least a 50% reduction in the number of draining fistulas at either Week 8, or for those patients receiving alternate blinded treatment, Week 16). There are a maximum of 8 patient evaluation visits in this study (Screen, Baseline, Week 4, Week 8, Week 12, Week 16, Week 20 and Week 24). Evaluations at most of these visits include a review of concomitant medications, medical history/adverse events, physical exam, fistula exam, blood draws for safety labs, urine pregnancy tests for females, and measurement of body weight. Patients will also be asked to keep a daily diary to record frequency of bowel movements, general well-being, and use of antidiarrheal medication. Treatment failure in this study is defined by one or more of the following occurring prior to Week 8: * The need for additional therapies or dose increase for treatment of Crohn's disease, including an increase of corticosteroid dose to higher than baseline * Clinical/symptomatic development of an abscess * Clinical/symptomatic evidence of stricture * The need for surgical intervention for Crohn's disease * The patient withdraws from the study Patients will be discontinued from the study at any time if one or more of the following complications occur: * Development of an abscess or symptomatic stricture * The need for surgical intervention for Crohn's disease * Occurrence of any other event that in the opinion of the investigator warrants discontinuation of the patient from the study In addition, patients whose CDAI score has risen by \> or = 70 points above baseline or risen above 400 will be discontinued from the study. Administration of any additional therapies or dose increases of concomitant medications (including corticosteroids) to control Crohn's disease to higher than baseline while receiving study drug (initial randomized treatment or alternate blinded treatment) will require discontinuation of the patient from the study. Discontinued patients will be evaluated in a termination visit to document the lack of treatment efficacy and no further study treatment will be given.