Study Length and Visits

The study will involve approximately 320 participants with recurrent Clostridium difficile infection. If you enter and complete the entire study, your participation in the study will last about 27 weeks. This includes:

  • A screening process to determine your eligibility for the study

  • Treatment with the oral capsule or placebo (3 in clinic or home visits; taking four capsules once a day for 3 days)

  • Follow-up period to check your health and well-being (three clinic visits and regularly scheduled telephone calls)

  • In total, the study involves 6 clinic visits (2 can be home visits) and up to 12 phone calls, in a 27-week period.

  • If your CDI comes back during the first eight weeks of the study, you may have the opportunity to participate in another, non-blinded extension study in which you would receive SER-109 and be monitored for about 27 additional weeks. You would sign a separate informed consent form for this extension study.

During the study clinic visits and phone calls, the study team will check on the subject’s symptoms and overall health using standard medical tests and procedures including:

  • Review of the subject’s medical history
  • Standard health tests (vital signs measurement, electrocardiogram, physical examination)
  • Collection of blood, stool, and urine samples
  • Evaluations of the subject’s diarrheal episodes
  • Pregnancy tests (for females, if necessary)
  • Discussions with the Study Team about the subject’s symptoms and recent medication use.
Can I Take Part?


  • Seres Therapeutics (Study Protocol, 20170324 Poster English20170324V1SERES-012RecruitmentBrochureEnglishCMcG, Seres 012PosterEnglish CLIENT REV & QD TRKED.DOCX)