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October 10, 2026
Antibiotics are among the most important medications in modern medicine. They treat bacterial infections that once caused serious illness or even death. However, while antibiotics eliminate harmful bacteria, they can also affect the beneficial bacteria that naturally live in the digestive tract. One of the most common side effects is antibiotic-associated diarrhoea.
Many people experience loose stools while taking antibiotics or within several weeks after completing treatment. In most cases, the condition is mild and resolves on its own. However, some cases can become severe and may signal a more serious infection, requiring prompt medical attention. Understanding why antibiotic-associated diarrhoea happens, recognizing the warning signs, and knowing when to seek medical care can help prevent complications and support faster recovery.
Antibiotic-associated diarrhoea (AAD) refers to diarrhoea that develops during antibiotic treatment or shortly after completing a course of antibiotics. It occurs because antibiotics disrupt the normal balance of bacteria in the intestines.
A healthy gut contains trillions of beneficial microorganisms that aid digestion, strengthen the immune system, and prevent harmful bacteria from multiplying. When antibiotics reduce these healthy bacteria, the digestive system becomes less stable, allowing harmful organisms to grow or altering the way the bowel functions.
Most episodes are mild, but a small proportion result from an overgrowth of Clostridioides difficile (formerly Clostridium difficile), commonly known as C. difficile. This infection can cause severe inflammation of the colon and requires immediate medical treatment.
Studies estimate that around 5% to 35% of people who take antibiotics may develop diarrhoea, although the likelihood varies depending on the individual and the type of antibiotic used. Some antibiotics can disrupt the natural balance of bacteria in the intestines, allowing digestive symptoms to develop during or shortly after treatment. The risk may be influenced by the specific antibiotic, the length of treatment, age, existing medical conditions, previous antibiotic use, and recent hospitalization. People who have taken multiple courses of antibiotics or have other health conditions may be more susceptible.
In Malaysia, antibiotics are commonly prescribed for bacterial infections affecting the respiratory tract, urinary tract, skin, and teeth. Understanding that diarrhoea can be an antibiotic-related side effect can help patients recognise changes in bowel habits early and seek medical advice when symptoms are persistent, severe, or accompanied by other concerning symptoms.
The human gut microbiome is a complex ecosystem containing beneficial bacteria that help digest food, produce vitamins, and protect against harmful microbes. Antibiotics cannot always distinguish between harmful and beneficial bacteria. As a result, they reduce the population of healthy bacteria, allowing changes that may lead to:
These changes contribute to loose stools and digestive discomfort.
Although any antibiotic may trigger diarrhoea, some medications carry a higher risk. The likelihood also increases when patients receive multiple antibiotics or prolonged treatment.
| Antibiotic Class | Examples | Relative Risk |
|---|---|---|
| Clindamycin | Clindamycin | Very High |
| Penicillins | Amoxicillin, Amoxicillin-clavulanate | High |
| Cephalosporins | Cefuroxime, Ceftriaxone | Moderate to High |
| Fluoroquinolones | Ciprofloxacin, Levofloxacin | Moderate |
| Macrolides | Azithromycin, Clarithromycin | Moderate |
Symptoms of antibiotic-associated diarrhoea often begin within several days of starting treatment, although they can sometimes develop up to eight weeks after the antibiotics have been completed. Common symptoms include loose or watery stools, more frequent bowel movements, abdominal cramps, bloating, increased urgency to pass stool, and mild nausea. In many cases, the symptoms are mild, and patients may otherwise feel well without significant changes in their overall health.
Not all diarrhoea is harmless. Seek medical care immediately if you experience the following. These symptoms may indicate C. difficile infection or another serious intestinal condition.:
C.difficile is a bacterium that can multiply after antibiotics disrupt the normal gut flora. It produces toxins that damage the lining of the colon, causing inflammation known as pseudomembranous colitis. Symptoms may include profuse watery diarrhoea, fever, severe abdominal pain, loss of appetite, nausea, elevated white blood cell count and dehydration.
Without appropriate treatment, severe infection may lead to complications including toxic megacolon, bowel perforation, sepsis, and, in rare cases, death. Older adults, hospitalized patients, individuals with weakened immune systems, and those taking repeated antibiotic courses face a higher risk.
Several factors increase the likelihood of developing antibiotic-associated diarrhoea. These include:
Understanding these risks helps healthcare professionals tailor treatment and monitoring.
Diagnosis begins with a detailed medical history and physical examination. Your doctor will ask about recent antibiotic use, when the symptoms started, how frequently you are passing stools, and whether you have fever, abdominal pain, recent hospitalisation, or are taking other medications. If symptoms are severe or persistent, further tests may be recommended, including stool tests for C. difficile toxins, stool cultures, blood tests, and, in selected cases, a colonoscopy. Early diagnosis is particularly important when a serious infection is suspected, as prompt treatment can help prevent complications.
Most mild cases of antibiotic-associated diarrhoea improve within a few days after completing treatment. Management usually focuses on staying hydrated with plenty of fluids or oral rehydration solutions when needed, eating easily digestible foods, and avoiding alcohol, greasy foods, and spicy meals. Patients should not stop or change prescribed antibiotics without first consulting their healthcare provider.
If symptoms are significant, your doctor may adjust or stop the antibiotic when appropriate, or prescribe targeted treatment for C. difficile. Hospitalisation may be necessary if severe dehydration or complications develop. Treatment depends on the severity of symptoms and the underlying infection.
Research suggests that certain probiotic strains may modestly reduce the risk of antibiotic-associated diarrhoea in some patients, particularly when started early during antibiotic therapy. The strongest evidence supports specific strains including:
However, probiotics are not suitable for everyone. Patients with severely weakened immune systems or critical illness should only use probiotics after discussing them with their healthcare provider because rare bloodstream infections have been reported.
The most effective prevention begins with responsible antibiotic use. Patients can reduce their risk by:
Healthcare providers also play an important role by practicing antibiotic stewardship and prescribing antibiotics only when clinically indicated.
Most cases resolve without complications, but medical assessment is recommended if diarrhoea is severe or persists for more than two to three days, or if you develop blood in the stool, fever, or signs of dehydration. You should also seek medical advice if symptoms begin after hospitalisation or several weeks after completing antibiotics. Prompt evaluation can help identify serious infections early and reduce the risk of complications.
Antibiotic-associated diarrhoea is a common side effect that results from changes in the balance of healthy bacteria in the gut. While most cases are mild and improve without lasting problems, persistent or severe diarrhoea should never be ignored. In some patients, it may indicate a serious Clostridioides difficile infection that requires urgent medical treatment.
Using antibiotics responsibly, staying hydrated, recognizing warning signs early, and seeking medical advice when symptoms worsen can significantly reduce the risk of complications. If you develop diarrhoea during or after a course of antibiotics, consult your healthcare provider rather than stopping your medication on your own.
Disclaimer: This article is for general information only and does not replace professional medical advice, diagnosis, or treatment. If you develop severe or persistent diarrhoea, seek medical advice promptly for appropriate assessment and care.
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