Antibiotics are among the most important medications in modern medicine. They can treat bacterial infections that might otherwise have a serious course. At the same time, however, they can also affect something that at first glance seems unrelated to infection — the gut microbiome. And this is where problems such as diarrhea or longer-term disruption of intestinal balance may arise.
What Is the Gut Microbiome and Why It Matters
The gut microbiome consists of a vast number of microorganisms involved in digestion, protection of the intestinal lining, and regulation of the immune system. When this system is in balance, it functions as a natural barrier against the overgrowth of undesirable microbes and helps maintain a stable intestinal environment.
Disruption of this balance — known as dysbiosis — can lead to digestive problems, more frequent infections, and in some individuals, longer-term health issues.
How Antibiotics Affect the Gut
Antibiotics are not “smart” — they do not distinguish between harmful bacteria and those that are beneficial to us.
Research shows that even short-term antibiotic treatment can lead to a rapid decrease in the diversity of gut bacteria. This effect has been observed in healthy volunteers, and in some of them the composition of the microbiome did not return to its original state even after several months. Reduced microbial diversity means weakened so-called colonization resistance - the natural ability of the microbiome to prevent the overgrowth of unwanted microorganisms.
Antibiotic-Associated Diarrhea as a Clinical Manifestation of Dysbiosis
One of the most common consequences of microbiome disruption is antibiotic-associated diarrhea (AAD). In most people, AAD has a mild course — loose stools, occasional abdominal pain, and bloating. Its development is often linked to direct disruption of the intestinal microbial environment.
As a result of antibiotic therapy, changes occur in the activity of intestinal bacteria, which may manifest as reduced production of short-chain fatty acids, impaired carbohydrate metabolism, and alterations in bile acid transformation. These processes can affect the intestine’s ability to maintain fluid balance and may lead to diarrhea.
In severe cases, antibiotic-induced dysbiosis may progress to antibiotic-associated colitis, with the most serious form being pseudomembranous colitis, which is associated with activation of the bacterium Clostridioides (Clostridium) difficile. Following antibiotic treatment, activation of other microorganisms that can cause similar digestive symptoms has also been described, such as Clostridium perfringens, Staphylococcus aureus, Klebsiella oxytoca, yeasts of the genus Candida, or Salmonella spp.
Christoph Högenauer, Heinz F. Hammer, Krejs G. J., Reisinger E. C. Mechanisms and Management of Antibiotic-Associated Diarrhea // Clinical Infectious Diseases. 1998; 27: 702–710.
What May Help Reduce the Risk of Problems
1. Rational Use of Antibiotics
Prevention of intestinal complications begins with the proper indication of antibiotic therapy. Antibiotics are intended for the treatment of bacterial infections, and their use should always be based on clinical assessment. The necessity and duration of treatment are important not only for therapeutic effectiveness but also for the risk of adverse effects, including impact on the intestinal environment.
2. Adequate Fluid Intake and a Gentle Diet
In the case of diarrhea, it is essential to ensure sufficient hydration and replenishment of minerals. The diet should be temporarily adjusted to current symptoms — simple, easily digestible, and free of strongly irritating components. The goal is to reduce the burden on the digestive tract and support gradual stabilization of bowel movements.
3. Probiotics and Prebiotics
In clinical practice, probiotics are often considered as an adjunct option during antibiotic treatment, particularly in connection with the occurrence of diarrhea. Their use is based on the assumption that they may influence the intestinal environment during periods when microbial balance is disrupted by antibiotics. However, the effect of probiotics may vary depending on the specific product, dosage, and individual patient characteristics. Therefore, probiotics cannot be regarded as a universal solution and do not replace medical evaluation in cases of severe or persistent symptoms.
4. Sorbents as Symptomatic Support
In clinical practice, enterosorbents are sometimes used to bind certain substances in the intestine and may help alleviate symptoms of diarrhea. It is important to understand them strictly as symptomatic support, not as a means to restore the gut microbiome or address the underlying cause of dysbiosis.
When using them, it is advisable to:
- maintain a time interval between sorbents and other medications to avoid reducing their absorption,
- not overestimate their effect and monitor symptom progression,
- seek medical attention if the condition does not improve or worsens.
When to Contact a Doctor Without Delay
Medical evaluation is particularly appropriate if:
- diarrhea persists for several days or appears after completing antibiotic treatment,
- fever, blood, or mucus in the stool occurs,
- significant weakness or signs of dehydration develop,
- abdominal pain is intense or progressively worsening.
Antibiotics are irreplaceable, but their impact on the gut should not be underestimated. They may temporarily disrupt the microbiome and, in some individuals, lead to diarrhea or dysbiosis. The risk can be reduced through prudent antibiotic use, early response to initial symptoms, and appropriate supportive care. The goal is not to “protect the gut at all costs,” but to minimize unnecessary interventions and allow the body the opportunity to regain balance.