Saturday, December 17, 2005

Antibiotic-associated diarrhea


Antibiotics first came into general use during World War II. Every American soldier was issued a first-aid kit containing sulfa powder, and the Allied forces who stormed Normandy carried penicillin. Since then, antibiotics have saved millions of lives. But like all drugs, antibiotics have side effects. One of the most common is antibiotic-associated diarrhea (AAD) — a potentially serious condition that affects up to 20 percent of people receiving antibiotic therapy.

AAD occurs when antibiotics disturb the natural balance of "good" and "bad" bacteria in your intestinal tract, causing harmful bacteria to proliferate far beyond their normal numbers. The result is often frequent, watery bowel movements.

Most often, the diarrhea is fairly mild and clears up shortly after you stop taking the antibiotic. But sometimes you may develop colitis, an inflammation of your colon, or a more serious form of colitis called pseudomembranous colitis. Both can cause abdominal pain, fever and bloody diarrhea. In cases of pseudomembranous colitis, these symptoms may become life-threatening.

Effective treatments exist for mild AAD, as well as for colitis and pseudomembranous colitis. In addition, taking concentrated supplements of beneficial bacteria (probiotics) may relieve symptoms or help prevent AAD in the first place.

Signs and symptoms

AAD can cause signs and symptoms that range from mild to severe. Most often, you'll have only a slight change in the bacteria in your digestive tract, which can cause loose stools or more bowel movements a day than are normal for you. If you develop these symptoms, they're likely to begin between the fourth and ninth days of therapy and to end within a few days to two weeks after you stop taking antibiotics. Sometimes, however, diarrhea and other symptoms may not appear for days or even weeks after you've finished antibiotic treatment.

When the overgrowth of harmful bacteria is severe, you may have signs and symptoms of colitis or pseudomembranous colitis, such as:

Frequent, watery diarrhea
Abdominal pain and cramping
Fever, often higher than 101 F
Pus in your stool
Bloody stools

You may not see an improvement until several weeks after you begin treatment for colitis or pseudomembranous colitis. And sometimes symptoms recur — usually within two months of the initial treatment — which means you may need to be treated a second or even a third time.


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 because they destroy beneficial bacteria along with harmful ones. Without enough "good" microorganisms, "bad" bacteriathat are resistant to the antibiotic you receivedgrow out of control, producing toxins that can damage the bowel wall and trigger inflammation.

The bacterium responsible for almost all cases of pseudomembranous colitis and many instances of severe AAD is Clostridium difficile. A small percentage of healthy people have C. difficile in their digestive tracts, but most people acquire the bacteria during a stay in a hospital or nursing home.

It's likely that many hospitalized patients 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.

What antibiotics cause AAD?

Virtually any antibiotic can cause AAD, colitis or pseudomembranous colitis, but the most common culprits are ampicillin, amoxicillin and clindamycin. Other antibiotics that have been especially implicated in pseudomembranous colitis include the cephalosporins cefuroxime (Ceftin) and cefpodoxime (Vantin). Sometimes erythromycins (Erythrocin), fluoroquinolones (Cipro, Floxin) and tetracyclines also can cause AAD. Problems can occur whether you take the antibiotics by mouth or receive them by injection.

Other effects of antibioticsIn 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.

Risk factors

Anyone who undergoes antibiotic therapy is at risk of AAD. But you're more likely to develop problems if you:

Are an older adult
Have had surgery on your intestinal tract
Have recently been in a hospital or nursing home, especially for several weeks

When to seek medical advice

Call your doctor right away if you experience the following signs and symptoms:

Several episodes of loose stools or watery diarrhea for two or more consecutive days

Abdominal pain or cramping
Pus or blood in your stool

These signs and symptoms may indicate a number of conditions, ranging from viral, bacterial or parasitic infections to inflammatory bowel disorders such as ulcerative colitis or Crohn's disease. In older adults with cardiovascular disease, low blood flow to the colon (ischemic colitis) also can cause these symptoms.

But if you're currently taking antibiotics or have recently finished antibiotic therapy, it's possible you have AAD. Your doctor can perform tests to determine the exact cause of your symptoms.

Have a serious illness such as cancer

Have a compromised immune system

Screening and diagnosis

To help diagnose AAD, your doctor will ask about your medical history, including whether you've had recent hospitalizations or antibiotic therapy. If your symptoms are severe, you'll also likely be asked to provide samples of your stool.

These are then checked in a laboratory for the presence of C. difficile. In a certain percentage of cases, a stool culture is falsely negative. This means that although C. difficile is present in your intestinal tract, it isn't detected by that test. Repeating the test may provide a more accurate result. You may also have a more sensitive test to check for toxins produced by C. difficile (cytotoxicity assay). Although it takes longer to obtain the results, this test is highly accurate in making the diagnosis.


Mild AAD isn't likely to cause any lasting problems. But pseudomembranous colitis can lead to life-threatening complications, including:

A hole in your bowel (bowel perforation). This results from extensive damage to the lining of your large intestine. The greatest risk of a perforated bowel is that bacteria from your intestine will infect your abdominal cavity (peritonitis).

Toxic megacolon. In this condition, your colon becomes unable to expel gas and stool, causing it to become greatly distended (megacolon). Signs and symptoms of toxic megacolon include abdominal pain and swelling, fever and weakness. You may also become groggy or disoriented. Left untreated, your colon can rupture, causing bacteria from your colon to enter your abdominal cavity. A ruptured colon requires emergency surgery and in some cases may be fatal.
Dehydration. Severe diarrhea can lead to excessive loss of fluids and electrolytes — substances such as sodium, potassium and chloride that are essential for transmitting nerve impulses, making your muscles contract and maintaining proper levels of fluid in and around your cells. Extreme fluid loss can cause seizures and shock — a condition in which your tissues don't receive enough oxygen. Symptoms of dehydration include a very dry mouth, intense thirst, little or no urination and extreme weakness.


If you have mild diarrhea, your symptoms are likely to clear up within a few days to two weeks after your antibiotic treatment ends. In the meantime, your doctor may recommend drinking plenty of liquids to prevent dehydration and avoiding foods that may aggravate your symptoms. When diarrhea is more severe, your doctor may stop your antibiotic therapy and wait for your symptoms to subside.

In cases of very severe diarrhea, colitis or pseudomembranous colitis, you're likely to be treated with the drug metronidazole (Flagyl), which is usually taken in tablet form for 10 days. If metronidazole isn't effective, or you're pregnant or breastfeeding, you'll receive another drug, vancomycin (Vancocin).

Both metronidazole and vancomycin are antibiotics that effectively control C. difficile. Vancomycin was once the drug of choice for treating AAD, but it's now usually reserved for the most resistant cases. It's also recommended for pregnant and lactating women because the effects of metronidazole on fetuses and infants aren't known.

Some people treated for pseudomembranous colitis have a recurrence of symptoms and need further treatment.

ProbioticsThe term probiotic means "for life." It generally refers to concentrated supplements of beneficial bacteria similar to those that occur naturally in your intestinal tract. Most probiotic supplements are formulated to survive the digestive process and the highly acidic conditions in your stomach.

Giving probiotic supplements to children receiving antibiotics can help prevent AAD. But the results of studies on adults have been mixed. Some studies have shown probiotic supplements to be effective in preventing or reducing the symptoms of AAD, while others have not. Anecdotal evidence indicates that instilling probiotics rectally may be more beneficial than taking them orally.

Probiotic formulas are available in liquid and capsule form in drugstores and natural food stores and in some grocery stores. Many need refrigeration. In addition, commercial yogurt labeled as having live cultures contains certain "good" bacteria, such as Lactobacillus acidophilus.
Another probiotic, the yeast Saccharomyces boulardii, has been shown to help protect against pseudomembranous colitis. This yeast, taken orally, is used in Europe to help prevent symptoms of AAD and may also prevent recurrences of the disease.

Capsules of S. boulardii are available in natural food stores and some drugstores. Although S. boulardii rarely causes side effects, avoid it if you have a yeast allergy. And if you have HIV/AIDS, talk to your doctor before trying this product.


The following suggestions may help prevent AAD or reduce its severity:

Take antibiotics only when you and your doctor feel it's absolutely necessary. Keep in mind that antibiotics won't help viral infections such as colds and flu.

Use antibiotics exactly as prescribed. Don't increase the dose, double up on missed doses, or take the medication longer than your doctor recommends.

Consider eating yogurt or taking probiotic capsules before, during and after antibiotic treatment.


If you develop AAD, colitis or pseudomembranous colitis, these dietary changes may help ease your symptoms:

Drink plenty of fluids. Water is best, but fluids with added sodium and potassium (electrolytes) may be beneficial as well. Avoid carbonated beverages, citrus juices, alcohol and caffeinated drinks such as coffee, tea and colas, which may aggravate your symptoms.

Emphasize soft, bland, easy-to-digest foods. These include rice, plain baked potatoes, yogurt and bananas. It's best to avoid most other fruits and their juices as well as dairy foods because they can make diarrhea worse.

Try eating several small meals. Space meals throughout the day instead of eating two or three large ones. Smaller servings are easier to digest.

Avoid certain foods. Stay away from spicy, fatty or fried foods and any other foods that make your symptoms worse.

Also, check with your doctor first before taking antidiarrheal medications, which may interfere with your body's ability to eliminate toxins and lead to serious complications.

Mayo Clinic

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