Antibiotic-Associated Diarrhea

Overview

Antibiotic-associated diarrhea is diarrhea that develops during a course of antibiotics or shortly after finishing one. While antibiotics work to clear harmful bacteria from the body, they can also affect the beneficial bacteria that live in the gut. When this balance is disturbed, the digestive system may not function as it normally would, and diarrhea can develop.

It is estimated that somewhere between five and twenty percent of people who take antibiotics may develop diarrhea as a result, though this figure can vary depending on which antibiotic is used, the person's age, and their overall health. In most cases the diarrhea tends to be mild and may clear up on its own once the antibiotic course is finished or within a few days of stopping.

In some cases, however, antibiotic use can allow a bacterium called Clostridioides difficile (also known as C. diff) to multiply in the gut in ways it would not normally be able to. This bacterium can cause intestinal inflammation and a considerably more serious form of diarrhea. C. difficile infection tends to be seen more frequently and can follow a more severe course in older people, those in hospital, and individuals with a weakened immune system.

Recognising antibiotic-associated diarrhea and knowing when to seek medical advice can help speed up recovery and prevent complications from developing.

Symptoms

The symptoms of antibiotic-associated diarrhea can range from a mild inconvenience to a quite serious illness. How severe the symptoms are tends to depend on what is causing them.

Possible symptoms of mild antibiotic-associated diarrhea include:

• Loose or watery stools several times a day. This is the most commonly reported symptom. Stools may become softer than usual or turn fully liquid. This can continue throughout the course of antibiotics and may settle within a few days of stopping.
• Abdominal cramps and wind. Changes in the gut flora can cause abdominal pain, cramping, and bloating.
• Mild nausea. Some people may notice a feeling of mild nausea alongside diarrhea when taking antibiotics.

Possible symptoms of the more serious C. difficile-associated form include:

• Very frequent, watery diarrhea. Loose stools occurring three or more times a day, and often much more frequently than that, may develop. This can lead to significant fluid loss from the body.
• Abdominal pain and tenderness. Noticeable pain, cramping, or tenderness when pressing on the abdomen may be present.
• Fever. A raised temperature is commonly seen with C. difficile infection and can be a sign that the situation is more serious than a straightforward case of diarrhea.
• Blood or mucus in the stool. The presence of blood or mucus in the stool can be a sign of intestinal inflammation and is worth getting assessed promptly.
• Nausea and loss of appetite. A general feeling of being unwell, nausea, and a reduced desire to eat may accompany more severe cases.

When to See a Doctor

Not every episode of diarrhea during antibiotics needs a doctor's visit, but some signs are worth paying attention to.

It is worth seeing a doctor if:

• Diarrhea continues for more than two days after finishing the antibiotic
• You are passing loose stools more than four times a day
• Abdominal pain is severe or persistent
• You have a fever alongside the diarrhea
• Signs of dehydration develop despite drinking plenty of fluids, such as dry mouth, dizziness, or noticeably reduced urine output
• You are elderly, a young child, or have a weakened immune system

Seek urgent medical attention or go to the emergency department if:

• There is blood or dark material in the stool
• You have a very high fever
• The abdomen feels very hard and is severely painful
• You feel faint or extremely weak
• You are unable to have a bowel movement but have severe increasing abdominal pain (this may suggest a bowel obstruction)

Causes

The underlying cause of antibiotic-associated diarrhea is the disruption antibiotics cause to the bacterial balance in the gut. Trillions of bacteria live in our intestines, and these bacteria may play an important role in digestive health, immune function, and overall wellbeing. Antibiotics target the bacteria causing an infection, but in doing so they can also affect many of these beneficial gut bacteria.

• Disruption of the gut flora. When the number of beneficial bacteria falls, the mechanisms that regulate bowel movements may be disturbed. Gut contents may pass through more quickly than normal and water may not be absorbed as efficiently, which can result in loose stools.
• C. difficile infection. Under normal circumstances, the beneficial bacteria in the gut help keep C. difficile from multiplying unchecked. When antibiotics reduce these protective bacteria, C. difficile may be able to grow in large numbers and produce toxins that irritate the lining of the intestine. This tends to be seen more often with broad-spectrum antibiotics, longer courses of treatment, and in hospital settings.
• Direct effects of the antibiotic on the gut. Some antibiotics may directly speed up intestinal movement. Certain antibiotics, including erythromycin and amoxicillin-clavulanate, are associated with a higher likelihood of causing diarrhea through this kind of direct effect.

Risk Factors

Factors that may increase the risk of antibiotic-associated diarrhea include the following:

• Broad-spectrum antibiotics. Antibiotics such as clindamycin, amoxicillin-clavulanate, cephalosporins, and fluoroquinolones affect a wider range of bacterial species, which may mean they disrupt the gut flora more significantly and carry a higher risk of causing diarrhea.
• Longer courses of antibiotics. The longer the course and the higher the dose, the greater the potential disruption to gut bacteria may be.
• Older age. People over 65 may be more likely to develop both antibiotic-associated diarrhea and C. difficile infection. The diversity of gut bacteria can decline with age, and immune responses may become less robust.
• Being in hospital. Hospital environments can harbour C. difficile spores, and people in hospital may have a higher risk of picking up this infection.
• A weakened immune system. Conditions or treatments that suppress the immune system, such as chemotherapy, long-term corticosteroids, or HIV, may reduce the gut's ability to defend itself against infection.
• A previous C. difficile infection. People who have had C. difficile before may have a higher risk of it recurring when they take antibiotics again.
• Taking proton pump inhibitors (acid-reducing medication). Some research has suggested a possible link between these medications and C. difficile risk, though this relationship is still being studied.

Diagnosis

In most cases, antibiotic-associated diarrhea can be identified through a clinical assessment. When C. difficile infection is suspected, some additional testing may be recommended.

• Medical history assessment. Your doctor will ask which antibiotic you have been taking, for how long, when the diarrhea began, and how it has been progressing. This information is often enough to guide the initial assessment.
• Stool test. If C. difficile infection is suspected, a stool sample can be tested to look for C. difficile toxins or the bacterium itself. This is among the most reliable ways to confirm a C. difficile diagnosis.
• Blood tests. If fever, significant abdominal pain, or a general decline in wellbeing is present, blood tests may be requested to assess markers of infection and inflammation.
• Colonoscopy or sigmoidoscopy. In severe cases, or when the diagnosis remains unclear, direct visualisation of the bowel wall may be considered. In C. difficile-related pseudomembranous colitis, characteristic changes to the bowel lining may be visible.

Treatment

The treatment approach depends on how severe the diarrhea is and whether C. difficile infection has been identified.

• Stopping or changing the antibiotic. In mild cases, stopping the antibiotic or switching to a narrower-spectrum alternative may resolve the diarrhea. However, you should not stop an antibiotic on your own without speaking to your doctor first — stopping treatment prematurely before the underlying infection is cleared can sometimes cause serious problems. This decision should always be made together with your doctor.
• Fluid and electrolyte replacement. Diarrhea can lead to significant loss of fluid and minerals from the body. Drinking plenty of water, diluted fruit juice, broth, or oral rehydration solutions available from a pharmacy can help replace these losses. In more serious cases, fluids given intravenously in hospital may be needed.
• Treatment of C. difficile infection. When C. difficile infection is confirmed, specific antibiotics that are effective against this bacterium are used. Vancomycin and fidaxomicin are among the options most commonly used for this purpose, and metronidazole may be considered in milder cases. Treatment typically lasts around ten to fourteen days.
• Probiotics. Some research suggests that probiotics may help reduce the risk of antibiotic-associated diarrhea when taken alongside a course of antibiotics. The strains with the most supporting evidence include Lactobacillus rhamnosus GG and Saccharomyces boulardii. However, probiotics may not be suitable for everyone and their effectiveness can vary, so it is worth discussing this with your doctor before starting them.
• Faecal microbiota transplantation (FMT). In cases of recurrent C. difficile infection where standard antibiotic treatment has not been sufficient, transferring gut bacteria from a healthy donor to the patient may be considered. This approach has been reported to produce very good results in recurrent C. difficile cases and may be an option in selected situations.
• Avoiding anti-diarrhoeal medications. Medications such as loperamide that slow bowel movements are generally not recommended in antibiotic-associated diarrhea, particularly if C. difficile is suspected. These medications can slow the passage of toxins through the bowel, potentially making things worse.

Living with Antibiotic-Associated Diarrhea and Prevention

Antibiotic-associated diarrhea cannot always be prevented, but there are steps that can help reduce the risk and support recovery.

Use Antibiotics Only When Genuinely Needed

Antibiotics are not effective against viral infections such as colds and flu, and unnecessary use can disrupt gut bacteria, increase the risk of diarrhea, and contribute to antibiotic resistance. Antibiotics should only be taken when your doctor has determined they are truly necessary.

Take Your Antibiotic as Prescribed

Stopping a course early can leave an infection incompletely treated and may increase the risk of more resistant infections in the future. Taking it for longer than needed can cause unnecessary disruption to the gut flora. Following the dose and duration your doctor has prescribed is the right approach.

Consider Probiotics

Taking a probiotic alongside your antibiotic course may help reduce diarrhea risk for some people. It is worth asking your doctor whether this might be appropriate for you.

Be Careful with What You Eat

While diarrhea persists, temporarily avoiding fatty, spicy, and high-fibre foods may reduce irritation to the gut. Easily digested foods such as plain rice, boiled potatoes, bananas, and plain cooked chicken may be better tolerated. Caffeine and alcohol can speed up bowel movements and are generally best avoided during this period.

Pay Attention to Hand Hygiene

C. difficile spores can survive in the environment for a long time and can be spread via hands or surfaces. Washing hands thoroughly with soap and water, especially after using the toilet, can help reduce this risk. Alcohol-based hand sanitisers may not be effective enough against C. difficile spores, so soap and water tends to be the preferred choice.

Preparing for Your Appointment

Having some information ready before seeing a doctor about antibiotic-associated diarrhea can help make the assessment process more straightforward.

What you can do:

• Note which antibiotic you are taking and for how long you have been taking it
• Record when the diarrhea started and roughly how many times a day you are having loose stools
• Observe the consistency, colour, and whether there is any blood or mucus in the stool
• Note whether you have a fever, abdominal pain, or any signs of dehydration
• List all current medications
• Mention if you have had a C. difficile infection before or have been in hospital recently

Questions you may wish to ask your doctor:

• Could this be caused by C. difficile?
• Is it safe to stop or change my antibiotic?
• Would taking a probiotic be helpful in my case?
• Which foods should I eat or avoid while this is going on?
• How can I tell if I am drinking enough fluids?
• How long might it be before things improve?

Questions your doctor may ask:

• Which antibiotic are you taking and for how long have you been on it?
• When did the diarrhea start and how many times a day is it happening?
• Have you noticed any blood or mucus in your stool?
• Do you have a fever?
• How severe is the abdominal pain?
• Have you been in hospital recently or are you currently in hospital?
• Do you have any condition or take any medication that affects your immune system?