This study is a phase II, randomized, double-blind, placebo-controlled study in patients diagnosed with Clostridium difficile associated disease. Patients with Clostridium difficile associated disease will be identified either from stool test results or by physician referral, and those who fulfill the eligibility criteria will be approached to participate. All study patients must receive standard of care treatment for Clostridium difficile associated disease. Enrolled patients will be randomized to receive a single intravenous solution of a human monoclonal antibody to C. difficile toxin A (GS-CDA1) combined with a human monoclonal antibody to C. difficile toxin B (MDX-1388) or 0.9% sodium chloride as placebo in a 1:1 treatment allocation. One hundred patients will be enrolled in the combination monoclonal antibody treated arm and 100 patients will be enrolled in the placebo arm. Patients will be evaluated through day 84 ± 10 days after receipt of study infusion for safety and clinical outcomes. Blood samples for safety analyses, anti-toxin A and anti-toxin B antibody measurements and human anti-human antibody (HAHA) titers will be collected at scheduled times. Study visits will occur on days 3 ± 1, 10 ± 2, 28 ± 3, 56 ± 7 and on day 84 ± 10 days. Occurrence of adverse events, use of concomitant medications, and record of stool output will be assessed at scheduled phone contacts and study visits. The first 20 patients enrolled will have a subsequent visit on day 168 ± 14 days for an additional blood collection for HAHA analysis.
