What Are Antibiotics? Appropriate Use and Antibiotic Resistance

Created: 17.11.2023 · Last Updated: 20.08.2026 · Category: Infectious Diseases and Internal Medicine · Prepared by the Academic Hospital Web and Editorial Board.

What Are Antibiotics?

Antibiotics are medicines used to treat certain bacterial infections. Some antibiotics kill bacteria, while others interfere with their growth, reproduction or essential functions.

The discovery of antibiotics was a major milestone in modern medicine. Alexander Fleming observed the antibacterial effect of penicillin in 1928, and its later development for clinical use transformed the treatment of bacterial infections.

Antibiotics are not necessary for every infection. The decision to prescribe one depends on the suspected cause and location of infection, severity, age, underlying medical conditions and, when appropriate, laboratory findings.

Which Infections Are Treated With Antibiotics?

Antibiotics should be used only for bacterial infections that are likely to benefit from antibiotic treatment.

They may be required for certain urinary tract infections, bacterial pneumonias, streptococcal throat infections, skin and soft-tissue infections and serious systemic bacterial infections.

Even some bacterial infections can improve without antibiotics. Treatment should therefore be determined after clinical assessment.

Do Antibiotics Treat Colds and Flu?

No. Antibiotics do not work against viruses.

They do not make influenza, the common cold or many other viral respiratory infections resolve more quickly.

Yellow or green nasal discharge or mucus alone does not mean that an antibiotic is required.

Antibiotics can be lifesaving when they are needed. When they are not needed, they provide no benefit while still exposing the patient to side effects and contributing to antibiotic resistance.

How Should Antibiotics Be Used?

  1. Do not start an antibiotic on your own. Similar symptoms do not necessarily have the same cause.
  2. Do not take antibiotics prescribed for someone else.
  3. Follow the prescribed dose and timing.
  4. Do not shorten or extend treatment on your own. Use the antibiotic for the duration prescribed by your healthcare professional.
  5. Do not save leftover antibiotics for a future illness.
  6. Do not share antibiotics with other people.
  7. Tell your healthcare professional about other medicines you use. Some antibiotics can interact with medicines or certain foods.

What Is Antibiotic Resistance?

Antibiotic resistance occurs when bacteria become resistant to one or more antibiotics.

It is the bacteria that become resistant, not the person taking the antibiotic.

When resistant bacteria cause an infection, medicines that previously worked may no longer be effective. This can limit treatment options and make infections more difficult to treat.

According to the World Health Organization's 2026 data, approximately 1 in 6 laboratory-confirmed common bacterial infections worldwide in 2023 was resistant to antibiotic treatment.

How Does Antibiotic Resistance Develop?

Bacteria can develop resistance through genetic changes or by acquiring resistance genes from other bacteria.

Antibiotic exposure creates selection pressure: susceptible bacteria may be eliminated while resistant bacteria survive and multiply.

Resistance can therefore be accelerated by unnecessary antibiotic use, inappropriate antibiotic selection, incorrect dosing or duration and inappropriate antimicrobial use in humans, animals and agriculture.

Resistant bacteria can spread between people, animals, food and the environment, making antimicrobial resistance a global public-health issue.

What Are the Risks of Unnecessary Antibiotic Use?

  • It contributes to antibiotic resistance.
  • It can cause medication side effects.
  • It can alter the microbiome.
  • It can contribute to diarrhea and yeast infections.
  • It can increase the risk of antibiotic-associated infections such as Clostridioides difficile.
  • Using the wrong antibiotic can delay correct diagnosis and treatment.
It is not accurate to say generally that antibiotics directly “weaken the immune system.” The main concerns with unnecessary use are adverse effects, changes to the microbiome and the development and spread of antibiotic resistance.

What Are the Side Effects of Antibiotics?

Side effects vary depending on the antibiotic and the individual.

Common effects can include nausea, diarrhea, gastrointestinal symptoms, skin rash and yeast infections.

Some antibiotics can also have medicine-specific effects involving the kidneys, liver, heart rhythm, nervous system or other organs. The safety profile is therefore not identical for every antibiotic.

What Should You Do if You Develop an Antibiotic Allergy?

Contact a healthcare professional if a new rash or other unexpected symptom develops during antibiotic treatment.

The following can indicate a serious allergic reaction and require urgent medical assessment:

  • Difficulty breathing
  • Swelling of the throat or tongue
  • Rapid swelling of the face, lips or mouth
  • Fainting or severe dizziness
  • Rapidly progressing widespread allergic symptoms

How Can Antibiotic Resistance Be Reduced?

  • Use antibiotics only when a healthcare professional determines they are needed.
  • Do not pressure a healthcare professional for an antibiotic prescription.
  • Follow the prescribed dose, timing and duration.
  • Do not share or save antibiotics for later use.
  • Practise appropriate hand hygiene.
  • Receive recommended vaccinations to help prevent infections and reduce the need for antibiotics.

Antibiotics Are Not Needed for Every Infection

Antibiotic treatment should be based on the cause of infection, the patient's clinical condition and, when appropriate, laboratory findings. Avoiding unnecessary antibiotic use helps protect both individual and public health.

Frequently Asked Questions

What are antibiotics?
Antibiotics are medicines used to treat certain bacterial infections. They can work by killing bacteria or interfering with their growth and reproduction.
Do antibiotics treat influenza?
No. Influenza is a viral infection and antibiotics do not work against viruses. If a bacterial infection develops in addition to influenza, a healthcare professional determines whether an antibiotic is required.
Can I stop an antibiotic when I feel better?
Do not change the duration of antibiotic treatment on your own. Follow the prescribed dose, timing and duration and do not independently shorten or extend treatment.
Does the person or the bacteria become resistant to antibiotics?
The bacteria become resistant. Antibiotic resistance does not mean that the person's body has become accustomed to the medicine. Some antibiotics may no longer work against infections caused by resistant bacteria.
Can leftover antibiotics be used later?
No. Leftover antibiotics should not be self-prescribed for a future illness or shared with another person. A future illness may have a different cause, and the wrong medicine can delay correct treatment.
Do antibiotics weaken the immune system?
It is not accurate to state generally that antibiotics directly weaken the immune system. Unnecessary antibiotic use can affect the microbiome, cause adverse effects and contribute to antibiotic resistance.
Can antibiotics cause serious side effects?
Yes. While many side effects are mild, serious allergic reactions, Clostridioides difficile infection and other antibiotic-specific serious adverse effects can occur.
Academic Hospital note: Antibiotic choice, dose and treatment duration vary according to the infection and the individual patient. Antibiotics left over from a previous illness or prescribed to someone else should not be used. You can book an appointment.

References

  1. Academic Hospital. Appropriate Antibiotic Use
  2. World Health Organization. Antimicrobial Resistance
  3. Centers for Disease Control and Prevention. Antibiotic Do's and Don'ts
  4. Centers for Disease Control and Prevention. Antibiotic Prescribing and Use