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Causes
By Mayo Clinic staff
Your digestive tract is a complex ecosystem that's home to millions of microorganisms (intestinal flora), including more than 500 species of bacteria. Many of these bacteria are beneficial, performing essential functions, such as synthesizing certain vitamins, stimulating your immune system, and helping protect you from harmful viruses and bacteria.
But some of the bacteria that normally inhabit your intestinal tract are potentially dangerous. They're 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, the bacteria that normally live in the colon, because they destroy beneficial bacteria along with harmful ones. 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.
Antibiotics first came into general use for soldiers during World War II. Since then, antibiotics have saved millions of lives. But like all drugs, antibiotics have side effects. And one of the most common is antibiotic-associated diarrhea, which affects up to one in five people receiving antibiotic therapy.
The usual suspect
The bacterium responsible for almost all cases of pseudomembranous colitis and many instances of severe antibiotic-associated diarrhea is Clostridium difficile. Most people acquire the infection during a stay in a hospital or nursing home after they've received antibiotics.
It's likely that many hospitalized people are exposed to C. difficile, but the bacterium causes problems only in people treated with antibiotics. Then it grows out of control, leading to severe diarrhea and potentially life-threatening complications.
Which antibiotics cause AAD?
Virtually any antibiotic can cause antibiotic-associated diarrhea, colitis or pseudomembranous colitis, but the most common culprits are ampicillin, clindamycin and cephalosporins such as cefpodoxime (Vantin).
Sometimes erythromycins (Erythrocin), quinolones (Cipro, Floxin) and tetracyclines also can cause antibiotic-associated diarrhea. Problems can occur whether you take the antibiotics by mouth or receive them by injection.
Other effects of antibiotics
In addition to disrupting the balance of microorganisms in your digestive tract, antibiotics can also affect the following:
- Rate of digestion. Antibiotics, such as erythromycin, can cause food to leave your stomach too quickly, causing nausea and vomiting. Other antibiotics may increase intestinal contractions, speeding up the rate at which food moves through your small intestine and contributing to diarrhea.
- Breakdown of food. Antibiotics may affect the way your body metabolizes fatty acids.
