Antibiotics are among the greatest medical discoveries of the 20th century. They have saved countless lives and made it possible to treat infections that were once often fatal. At the same time, however, they are not a miracle cure without their downsides. Time and again, it has become clear that antibiotics can cause serious side effects—from gastrointestinal complaints to impaired liver function to life-threatening allergic reactions. In this article, we take a comprehensive look at the worst side effects of antibiotics, explain the mechanisms behind them, and also examine the long-term consequences for the gut and oral microbiome.
Antibiotics - Between lifesaver and risk
Since the discovery of penicillin by Alexander Fleming in 1928, medicine has undergone revolutionary changes. Suddenly, it became possible to specifically combat bacterial infections. Diseases like pneumonia, scarlet fever, and wound infections lost their horror. But the widespread use of antibiotics also brought new problems: resistance on the one hand, and serious side effects on the other.
Today, doctors face the challenge of carefully weighing the benefits and risks. Although antibiotics are often essential, they can trigger processes in the body that seriously endanger the patient's life.
The worst side effects at a glance
Allergic reactions
One of the most dangerous side effects of antibiotics is allergic reactions. These are particularly common with penicillins and cephalosporins. While some people only develop an itchy rash, others can experience life-threatening anaphylactic shock.
Disturbance of the intestinal flora and Clostridioides difficile
Antibiotics not only work against pathogenic bacteria, but also kill many beneficial microorganisms. Infection with Clostridioides difficile , which can lead to severe diarrhea and pseudomembranous colitis, is particularly feared. The intestinal microbiome is crucial for digestion, the immune system, and metabolism. Antibiotics can drastically reduce the diversity of intestinal flora, which in the long term can increase the risk of chronic inflammatory bowel disease, allergies, or metabolic problems.
Effects on the oral microbiome
The oral microbiome is also affected. Disturbed oral flora can lead to oral thrush, periodontitis, and long-term dental problems.
Kidney damage
Some antibiotics, especially aminoglycosides, can damage the kidneys and, in severe cases, cause acute kidney failure.
Liver damage
Antibiotics such as macrolides or tetracyclines can trigger drug-induced hepatitis and, in severe cases, even acute liver failure.
Neurological complications
Fluoroquinolones are suspected of causing neurological disorders such as headaches, hallucinations or peripheral neuropathies.
Tendon and muscle damage
Fluoroquinolones can cause Achilles tendon inflammation and ruptures, especially in combination with cortisone preparations.
Changes in blood count
Various antibiotics can cause leukopenia, thrombocytopenia or anemia, which increases susceptibility to infection and bleeding.
Cardiac arrhythmias
Macrolides and fluoroquinolones can prolong the QT interval and cause risky cardiac arrhythmias.
Skin reactions and photosensitivity
Tetracyclines and sulfonamides can cause photosensitivity or severe skin reactions such as Stevens-Johnson syndrome.
Psychological side effects
Fluoroquinolones can promote depression, anxiety or psychosis.
Summary table
| Side effect | Typical triggers (antibiotic classes) | Severity | Possible consequences |
|---|---|---|---|
| Allergic reactions | Penicillins, cephalosporins | High | Anaphylaxis, respiratory arrest |
| Disturbance of the intestinal flora / C. diff | Broad-spectrum antibiotics | High | Severe diarrhea, pseudomembranous colitis |
| Changes in the intestinal microbiome | All classes, especially broad spectrum | Medium to high | Long-term dysbiosis, risk of chronic diseases |
| Changes in the oral microbiome | All classes | Medium | Oral thrush, periodontitis |
| Kidney damage | Aminoglycosides, cephalosporins | High | Acute renal failure |
| Liver damage | Macrolides, tetracyclines | Medium to high | Hepatitis, liver failure |
| Neurological problems | Fluoroquinolones | Medium to high | Neuropathy, seizures |
| Tendon and muscle damage | Fluoroquinolones | Medium to high | Achilles tendon rupture, restricted mobility |
| Changes in blood count | Different classes | Medium | Leukopenia, thrombocytopenia |
| Cardiac arrhythmias | Macrolides, fluoroquinolones | High | Ventricular fibrillation, sudden cardiac death |
| Skin reactions | Sulfonamides, tetracyclines | Medium to high | Photosensitivity, Stevens-Johnson syndrome |
| Psychological side effects | Fluoroquinolones | Medium | Depression, psychosis |
Conclusion
Antibiotics are undoubtedly life-saving, but their use carries risks that should not be underestimated. The most serious side effects range from life-threatening allergic reactions to organ damage and long-term changes in the microbiome.
Important points:
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Take antibiotics only when medically indicated and in the correct dosage.
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Patients should report possible side effects early.
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People with pre-existing medical conditions or who have repeatedly used antibiotics are particularly at risk.
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Intestinal and oral microbiomes can be affected in the long term – adjunctive probiotic therapy may be useful.
FAQ
Are all antibiotics equally dangerous?
No, each class has its own risks. Some side effects are closely linked to specific drugs, such as tendon damage with fluoroquinolones.
Can side effects be prevented?
Yes, through strict indication, correct dosage, avoidance of unnecessary broad-spectrum antibiotics and, if necessary, accompanying probiotics.
What effects do antibiotics have on the microbiome?
Both intestinal and oral flora can become imbalanced. This increases susceptibility to infections, digestive problems, and can promote chronic diseases in the long term.
What to do if side effects occur?
Report any unusual symptoms to a doctor immediately. If you experience shortness of breath, swelling, or allergic reactions, call emergency services immediately.
Are children particularly at risk?
Yes. Some antibiotics, such as tetracyclines, are contraindicated in children under 8 years of age. Children are often more sensitive to side effects.
Can you simply stop taking antibiotics?
No. Discontinuation should only be done in consultation with a doctor to avoid worsening the infection or promoting resistance.
