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Antibiotic-Associated Diarrhea (AAD)

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Antibiotic-Associated Diarrhea (AAD)

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Antibiotic-associated diarrhea is a common condition caused by taking antibiotics (medicines that kill bacteria). Read this article to know more about diarrhea caused by antibiotics.

Medically reviewed by

Dr. Lekshmipriya. B

Published At November 9, 2017
Reviewed AtMarch 18, 2024


The consequences of long-term antibiotic administration are diarrhea, antibiotic resistance, impaired immunity, increased cost of treatment, organ failures and deaths, and reduction in beneficial phytoestrogens.

Antibiotic-associated diarrhea (AAD) is unexplained diarrhea associated with the use of an antibiotic. AAD may occur up to two to three weeks following the cessation of antibiotic therapy rather than during the treatment. Antibiotics cause diarrhea due to infection by antibiotic-resistant pathogens such as Staphylococcus aureus, Clostridium difficile, Candida albicans, Clostridium perfringens type A, Klebsiella oxytoca. This article will mainly discuss the role of Clostridium difficile in causing antibiotic-associated diarrhea.

What Are the Antibiotics That Carry a High Chance of Causing Diarrhea?

Almost all the antibiotics tend to cause diarrhea. But there are a few antibiotics that tend to cause diarrhea and they are as follows.

  • Ampicillin and Amoxicillin are the types of penicillins and they are the most important ones to cause diarrhea.

  • Certain cephalosporins like Cephalexin.

  • Clindamycin.

What Is the Role of Clostridium Difficile in Antibiotic-Associated Diarrhea?

Clostridium difficile-associated disease (CDAD) is one of the most important causes of antibiotic-associated diarrhea. It is responsible for 15 to 25 percent of cases of AAD. CDAD is a serious condition with a mortality of up to 25 percent in frail elderly. The average age of those with Clostridium difficile infection is nearly 20 years older than the average age of those in hospitalization for other reasons. CDAD is defined as unexplained diarrhea occurring after two hours to within two months after antibiotic usage and is often accompanied by fever, abdominal pain, and cramps. CDAD is established when a toxin is identified in the stool, regardless of C.difficile isolation from the stool.

C. difficile is a spore-bearing, gram-positive bacterium, present in ample amounts in the environment. Spores of C.difficile are hard to eradicate as they are resistant to drying and heating, and also resistant to most antiseptic disinfectants. The ability to produce spores explains how the organism being fastidious anaerobic, can be acquired from the environment. Broad-spectrum antibiotics such as Clindamycin, Fluoroquinolones, Cephalosporins, etc. most often cause CDAD.

What Are the Causes of Antibiotic-Associated Diarrhea?

The exact cause of antibiotic-associated diarrhea is not fully comprehended. It is generally believed to occur due to a disruption in the balance of beneficial and harmful bacteria in the gastrointestinal tract caused by antibiotic medications.

Antibiotics across various classes are known to potentially trigger antibiotic-associated diarrhea. Specifically, the following antibiotic types are commonly associated with this side effect:

  • Macrolides.

  • Cephalosporins.

  • Fluoroquinolones.

  • Penicillins.

How to Diagnose the Presence of Clostridium Difficile?

The laboratory diagnosis is based on culture and toxin detection in fecal specimens. Culture is very sensitive, but if carried out without toxin testing, it may lead to misdiagnosis of CDAD as it detects even asymptomatic cases. C. Diff Quik Chek Complete® test is a rapid cassette assay that simultaneously detects both glutamate dehydrogenase (GDH) antigen and toxins A and B of C. difficile in fecal specimens.

The cultivation of the organism, though difficult, is considered the gold standard. Although stool culture has high sensitivity, as the rate of asymptomatic carriage of C.difficile among hospitalized patients is high, the specificity for CDAD is low. The disadvantage of the cell cytotoxicity neutralization assay (CCNA) is that it is technically demanding and has a relatively long turnaround time (24 to 48 hours). Although endoscopy is required for the specific diagnosis of PMC, it is an invasive test and not sufficient to diagnose all cases of CDAD. Newer methods like toxin detection by immunochromatography have a rapid turnaround time and are inexpensive.

Who Is at Risk of Acquiring Clostridium Difficile-Associated Disease?

C.difficile is acquired from the hospital environment. It causes an increased burden in terms of cost and health. The risk factors involved in the acquisition of CDAD are patients aged above 65 years, treatment with broad-spectrum antibiotics, exposure to an infant carrier or infected adult, tracheostomy, immunodeficiency, Ryle’s tube feeding, antacids, intestinal surgeries, chemotherapy, and chronic kidney disease.

C.difficile produces toxins that attack the lining of the intestine. Toxins A and B are the primary virulence factors contributing to the pathogenesis of CDAD, and the genes responsible for these toxins are TcdA and TcdB. The toxin expression is increased by antibiotic concentration. TcdA is a potent enterotoxin. TcdB is cytotoxic and is more potent (~1000 fold) than TcdA. Another toxin is the binary toxin encoded by genes ctdA and ctdB. CDAD may progress to a fatal condition known as pseudomembranous colitis (PMC) with rapidly fatal fulminant colitis and megacolon, resulting in death.

How to Manage Clostridium Difficile-Associated Disease?

The most crucial aspect in the management of CDAD is early identification of the disease and the discontinuation of the inciting agent, as it has the potential to emerge as an epidemic strain causing large hospital outbreaks. The treatment and isolation of infected cases decrease not only the treatment cost incurred by the patient but also reduce the morbidity and halt the spread of the disease in the community.

How to Prevent Antibiotic-Associated Bacteria?

There are a few ways to prevent antibiotic-associated diarrhea and they are,

  • Be careful with the prescription and medicines. Few medicines will be strictly advised to be taken along with food to avoid digestion issues.

  • Including probiotics in the daily diet, can bring in some good bacteria.

  • To prevent Clostridium difficile, proper hand hygiene has to be followed, especially after using restrooms.

  • Antibiotics are meant to kill the harmful bacteria and cure bacterial infections. Using antibiotics to cure colds will not work. Thus, antibiotics have to be used appropriately as overuse may cause antibiotic resistance and issues with the digestive system.

  • Informing the doctors that one had an experience of antibiotic-associated diarrhea will restrain the doctor from prescribing the same antibiotics again.

When Should a Person Seek Medical Attention?

Contact the doctor immediately if there are severe signs and symptoms of antibiotic-associated diarrhea. Since these symptoms can overlap with various conditions, the doctor may advise diagnostic tests, such as stool or blood tests, to identify the underlying cause.


Antibiotic-associated diarrhea is a common condition but has to be kept in mind. So that future usage of the same antibiotics can be avoided. The best way to cope with diarrhea is to drink lots of fluids to remain hydrated. One way to combat antibiotics-associated diarrhea is to reduce the intake of fiber foods. Foods that may worsen diarrhea should be strictly avoided. Creamy foods, dairy products, sugars, and sweets can be avoided. Consulting with a doctor if the diarrhea does not cease, is very important. Otherwise, the affected individual may become extremely weak

Frequently Asked Questions


How to Treat Antibiotic-Associated Diarrhea?

To treat antibiotic-associated diarrhea, the following can be practiced:
- Discontinuing the antibiotics.
- Changing the medications. 
- Giving probiotic supplements


What Do You Mean by Antibiotic-Associated Diarrhea?

Antibiotic-associated diarrhea (AAD) is unexplained diarrhea that occurs with antibiotics. Sometimes, AAD may also be associated with a clostridium difficile infection. This infection constitutes only a small percentage of AAD.


What Are the Antibiotics That May Cause AAD?

The antibiotics that may cause AAD may include:
- Cephalosporins.
- Fluoroquinolones.
- Amoxicillin.
- Ciprofloxacin.
- Ampicilli


Which Is the Best Probiotic for AAD?

Probiotics are quite effective in treating antibiotic-associated diarrhea. The best probiotics that are used in the treatment of AAD include:
- Lactobacillus rhamnosus G.
- Saccharomyces boulardii.
- Lactobacillus casei.


Why Are Broad Spectrum Antibiotics Known to Cause Diarrhea?

Broad-spectrum antibiotics are known to cause diarrhea in almost 30 % of the treatment cases. This is because broad-spectrum antibiotics can even kill normal gut flora. These gut flora or microorganisms generally protect the gut from harmful substances.


Does Antibiotics Cause Colitis?

Inflammation of the colon may be known as colitis. Almost all antibiotics are known to cause colitis. Antibiotics such as Amoxicillin, Fluoroquinolones, and Penicillin have more chance of causing colitis. However, these symptoms usually reduce in a week or ten days after stopping the medications.


How Long Does AAD Take To Develop?

AAD may start as soon as one week after commencing the antibiotic medication. After starting the medication, it is referred to as a condition with loose and watery stools. The symptoms gradually disappear after stopping the medications.


Should Antibiotics Be Stopped if You Get Diarrhea?

Stopping the drug depends on the severity of the condition. If the condition is quite severe, the Doctor may ask you to stop taking the medication or give an alternative medication. But if the condition is not that severe, then diarrhea may subside within a few days. The doctor may also substitute the medication with probiotics.


What Happens if You Do Not Take Probiotics Along With Antibiotics?

If you don't take probiotics along with antibiotics, it may cause diarrhea. Antibiotics, especially broad-spectrum antibiotics, are known to cause diarrhea as they disrupt the gut microbial flora.
Hence probiotics are mostly given as a supplement to antibiotics.


Does Amoxicillin Cause Diarrhea?

Diarrhea can be one of the side effects of amoxicillin. Amoxicillin is an antibiotic that belongs to the macrolides group of antibiotics. Diarrhea due to Amoxicillin may not necessarily occur in everyone. It is advisable to keep yourself hydrated to get over this.


What Causes Watery Stools or Diarrhea?

Watery stools or diarrhea can be caused by
- Infection.
- Food poisoning.
- Medications such as antibiotics.


What Are the Side Effects of Antibiotics?

The side effects of antibiotics can include:
- Vomiting.
- Nausea.
- Diarrhea.
- Bloating and constipation.
- Stomach ache.
- Loss of appetite.
Source Article IclonSourcesSource Article Arrow
Dr. Geethu Thomas
Dr. Geethu Thomas

Family Physician


chronic kidney diseasediarrheaantibiotic-associated diarrheaclostridium difficile infection
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