Antibiotic-associated diarrhea occurs when antibacterial medications (antibiotics) upset the balance of good and bad bacteria in your gastrointestinal tract.

The antibiotics most likely to cause diarrhea

Nearly all antibiotics can cause antibiotic-associated diarrhea, colitis or pseudomembranous colitis. The antibiotics most commonly linked to antibiotic-associated diarrhea include:

  • Cephalosporins, such as cefixime (Suprax) and cefpodoxime
  • Clindamycin (Cleocin)
  • Penicillins, such as amoxicillin (Amoxil, Larotid, others) and ampicillin
  • Fluoroquinolones, such as ciprofloxacin (Cipro) and levofloxacin (Levaquin)

How antibiotics cause diarrhea

Your digestive tract is a complex ecosystem that's home to millions of microorganisms (intestinal flora), including hundreds of species of bacteria. Many of these bacteria are beneficial, performing essential functions.

But some of the bacteria that normally inhabit your intestinal tract are potentially dangerous. These harmful bacteria are usually kept in check by beneficial bacteria unless the delicate balance between the two is disturbed by illness, medications or other factors.

Antibiotics can be especially disruptive to intestinal flora because they destroy beneficial bacteria along with harmful ones. Sometimes, without enough "good" microorganisms, "bad" bacteria that are resistant to the antibiotic you received grow out of control, producing toxins that can damage the bowel wall and trigger inflammation.

Clostridium difficile causes most serious antibiotic-associated diarrhea

The bacterium responsible for almost all cases of pseudomembranous colitis and many instances of severe antibiotic-associated diarrhea is C. difficile. Most people acquire a C. difficile infection during a stay in a hospital or nursing home after they've received antibiotics.

Jun. 11, 2013