Pseudomembranous colitis is a infection of the colon caused by the bacterium Clostridium difficile. The illness is characterized by diarrhea, fever, and abdominal pain. It can be severe and even fatal.

In most cases the patient had recently been on antibiotics. Antibiotics disturb the normal bowel bacterial flora that generally keeps the bacteria Clostridium difficile under control. Clindamycin is the antibiotic associated with this disorder classically, but any antibiotic can cause the condition. Additional groups at increased risk are diabetics and the elderly. Half of cases are not associated with risk factors.

The disease is ususally treated with metronidazole. Oral vancomycin is an alternative drug. Occasionally metronidazole has been associated with the development of pseudomembranous colitis. In these cases metronidazole is still effective treatment, since the cause of the colitis is not the antibiotic, but rather the change in bacterial flora from a previous round of antibiotics. If antibiotics do not control the infection the patient may require a colectomy (removal of the colon) for treatment of the colitis.