What are antibiotics, types and main examples


What are antibiotics?

Antibiotics are drugs used specifically for the elimination of bacteria without damaging the cells of our body. There are several different types of antibiotics to have an effect on all types of bacteria harmful to our body. They are drugs that work exclusively on bacteria  and are not able to eliminate viruses and fungi.

The first antibiotic discovered was penicillin. She was discovered by accident by British microbiologist Alexander Fleming. He was doing studies looking for a way to prevent bacterial infections.

He took a vacation in August 1928 and forgot to refrigerate some of the bacterial sample plates. The next month, when he returned to work, he found the sample contaminated by mold. When he was about to discard the sample, a colleague visited him and asked about the research.

Fleming used the samples he had to explain the work and realized that in one of them, there was a transparent circle around the mold that contaminated the bacteria, indicating that it produced a bactericidal substance.

After taking samples of the mold and carrying out further tests, penicillin, the first antibiotic, was produced for the first time.

How do they work?

Bacteria invade the host’s body and use the body’s resources to reproduce, doubling in quantity with each cycle of reproduction, which can last a few hours or a few minutes.

When they reach a certain number, they begin to damage the body, changing the environment around them. The immune system is then activated and wages a battle with the bacteria, seeking to eliminate the infection.

Often, the battle can last for days and the body is not always able to win. When this happens, the bacteria kill the host.

Sometimes the body may even be able to eliminate the bacteria, but depending on how strong the immune system or bacteria are, there may be sequelae in the body. That’s where antibiotics come in: they help the body.

Each type of antibiotic has a different effect and not all bacteria are sensitive to every antibiotic. Some types work by killing bacteria and some prevent their reproduction, preventing them from multiplying and conquering the body. The immune system then manages to kill the few surviving bacteria and those that are no longer reproducing.

Action types

Modern antibiotics can be divided into two types, depending on how they work. Are they:


Bactericides are antibiotics that kill bacteria. They can do this in a number of ways, dramatically reducing their numbers and making everything easier for the immune system.

There are several ways that an antibiotic can kill bacteria. Penicillin, for example, does so by destroying the cell wall of bacteria and preventing their synthesis, killing them. Another way used by antibiotics to kill bacteria is to inhibit the production of folic acid . Without this substance, the bacterium dies.


Bacteriostats are antibiotics that prevent bacteria from reproducing. Thus, the number of bacteria stops growing, and then they start to die naturally and be killed by the immune system, without overloading it.

Bacteriostats prevent bacteria from multiplying. They can inhibit cell protein synthesis , which prevents them from dividing. They can also prevent the duplication of the bacterium’s DNA, which stops them from multiplying, allowing the immune system to eliminate them efficiently.

Some deodorants use bacteriostatic chemicals, preventing bacteria that may be present in sweat from multiplying and emitting odors.

Types of antibiotics

There are several varieties of antibiotics that are used for different types of infection.

Antibiotics are separated according to their chemical structures and mechanisms of action. The classifications are as follows:


Used to treat severe infections by gram-negative bacteria like Escherichia coli . It can cause toxicity of the vestibulocochlear nerve. Aminoglycoside antibiotics penetrate the bacteria and inhibit its protein synthesis, killing it. One of the representatives is neomycin .


This antibiotic was developed for the reduction of tumor cells. Although antibiotics act on bacteria, it attacks tumors using the same mechanism used to kill microbes.

It is still in the experimental stage. It can cause toxicity of the liver, kidneys and gastrointestinal system. One of the representatives is herminicin .


Used for respiratory and urinary infections. It can be represented by loracarbefe .


A broad-spectrum antibiotic, it is used for both gram-positive and gram-negative bacteria. It prevents bacterial cell division by inhibiting cell wall production. One of the representatives is the meropeném .

Cephalosporins (first to fifth generation)

Cephalosporins are divided into several generations. Each has some differences from the previous one, often in its effectiveness against resistance.

Third-generation cephalosporins, for example, are effective in gram-positive and gram-negative bacteria and are often used in hospital infections, which are often resistant to various antibiotics because of their breeding ground.

The fourth generation have the same effect, but they are even more effective against gram-positive bacteria and more effective against bacteria resistant to the third generation.

Cephalosporins can be represented by cephalexin , from the first generation.


Used in severely ill patients with hypersensitivity to beta-lactam antibiotics, such as penicillins and cephalosporins. A glycopeptide is teicoplanin .


Used against Lyme disease and syphilis infections . Some macrolides can be used against pneumonia . The azithromycin  is one of the representatives.


Used against aerobic gram-negative bacteria, such as enterobacteria. They are inactive against gram-positive and anaerobic bacteria. The aztreonam  represents a monobactam.


Penicillins are used against many types of infections. They were the first antibiotics and have a broad spectrum of action. The amoxicillin  is part of this group.

Polypeptide antibiotics

It can be used in cases of eye and urinary infections. The colistin , which belong to this group, is used to fight hospital infections because, due to their little use, few bacteria have developed resistance to it.


Used in urinary tract infections, bacterial diarrhea , prostatitis caused by bacteria and gonorrhea , among others. Represented by ciprofloxacin .


This type of antibiotic is used against urinary and salmonella infections. The sulfadimethoxine  part of this group.


Infections with chlamydia, syphilis and acne can be treated by tetracyclines, among others. The tetracycline  part of this group and is the antibiotic that gives its name.


Used to prevent infections after surgery and to treat acne. The lincomycin part of this group.

Various antibiotics

Each of these classes has several different antibiotics. They act similarly within their own class, but each class acts differently from the other. Some are more aggressive and cause different side effects or are even capable of causing damage to the body.

There are also antibiotics that do not fit into any of these classifications, as is the case with ethambutol , an antibiotic used for the treatment of tuberculosis and that acts by inhibiting the formation of the bacterial cell wall.

Most used

The most widely used antibiotics are as follows:

  • Ciprofloxacin;
  • Amoxicillin;
  • Ampicillin;
  • Azithromycin ;
  • Cephalexin ;
  • Tetracycline


NEVER  self-medicate or stop using a medication without first consulting a doctor. Only he will be able to tell which medication, dosage and duration of treatment is the most suitable for his specific case. The information contained in this website is only intended to inform, not in any way intended to replace the guidance of a specialist or serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.

How to know which antibiotic is best?

Only the doctor will be able to indicate which antibiotic is best for you.  Contact your doctor if you believe you are dealing with a bacterial infection.

One of the main methods for choosing the antibiotic that will be used in each bacterium is the Gram technique, but a bacterial culture may also be needed to determine the appropriate drug.

Gram’s technique

Gram’s technique was developed in the late 19th century by Hans Christian Joachim Gram, a Danish physician. The technique involves coloring the bacterium’s cell walls with a violet dye and a fixative, the lugol.

Both gram-negative and gram-positive bacteria absorb the dye and lugol in an identical manner and take on a violet color. So 95% ethanol or acetone is used in the bacteria.

In the case of gram-negative bacteria, the walls are dissolved and the stain is eliminated. In gram-positive cells, the cell walls contract, making them impermeable, and the color remains the same.

Finally, another dye, fuchsin, is used. When looking at the result under a microscope, the gram-positive bacteria will appear violet in color. Gram-negatives will be red or pink.

This test is able to indicate whether that specific bacterium has thinner and more sensitive (gram-negative) or thick and resistant (gram-positive) cell walls to decide what type of antibiotic can be used.

Bacterial culture

In addition to the Gram technique, other tests must be done to identify which bacteria are present and what type of antibiotic is effective in it. Some bacteria can be resistant strains and tests are needed to find the ideal type of medicine.

For this, bacterial cultures are performed. A sample of the bacteria is collected, which is placed in an environment conducive to their reproduction. When there are enough bacteria, you can identify them and test them with a number of different antibiotics to find out which ones work or don’t work on that specific bacterium.


Bacteria are the smallest type of living thing that exists. Most of them are harmless to humans. Trillions of them live in your body, living harmlessly in you, under control of the immune system.

However, some of them can be harmful and, until the development of the first antibiotic, infections caused millions of deaths, since the cure depended completely on the patient’s immune system.

In the past, tuberculosis was a death sentence and a cut on the hand could easily lead to the end of a life. Antibiotics have saved millions of people over the years and, along with vaccination, have been milestones in modern medicine. It was believed that, thanks to them, we would eliminate all diseases caused by bacteria, but that was not quite what happened.


Bacteria are living beings and, like us, are subject to adaptations to the environment. Antibiotics make the environment extremely hostile to bacteria, but they are not able to eliminate 100% of them.

Usually, this is not a problem, since the immune system itself usually takes care of the few survivors, but when an antibiotic-resistant bacterium escapes, it can reproduce.

Thus, a new infection can begin and this time it will be immune to the antibiotic, since the bacteria of the new infection are descendants of a resistant bacterium.

Currently, antibiotics from the same family as penicillin (now called penicillins ) are used, but the penicillin itself, discovered by Fleming, barely appears. This is because most of the bacteria in the world have developed resistance to penicillin.

In addition, some bacteria are able to transfer their immunity to other living bacteria, and some can collect DNA from dead bacteria and absorb their resistance. This can happen even between different species of bacteria, creating a superbug , resistant to several antibiotics.


Superbacteria are resistant to several antibiotics. They can be created through natural mutations or, more commonly, the misuse of antibiotics .

Antibiotics are prescribed in specific doses and for specific times because these are the doses and the time needed for the infection to be eliminated.

Many people stop taking the antibiotic when they notice that the symptoms are gone, but that just means that the amount of bacteria present is no longer enough to cause symptoms.

In a 10-day antibiotic treatment, the least resistant bacteria can die on the first day, while the most resistant bacteria can die on the seventh day. However, if the patient stops taking the antibiotic on the fifth day, the most resistant will stay alive.

They will have been exposed to the antibiotic and may develop resistance to it. After that, they multiply, spreading the resistance, and when the disease returns, the same antibiotic will have no effect.

When this type of behavior is repeated very often, the various generations of bacteria, which spread around the world around the infected person, acquire different resistances.

This is especially common in hospitals, where bacteria can be exposed to a variety of patients, antibiotics and other bacteria that can transfer their resistance to one another.

Emergency antibiotics

To deal with resistant bacteria, several different types of antibiotics are used, in addition to some that are controlled for specific use against bacteria resistant to various antibiotics. There are rules for using them, to avoid creating a superbug that is immune.


Colistin is an emergency antibiotic that was discovered in 1959, but little used because it causes liver damage. Therefore, few bacteria are resistant to it, and in cases of bacteria immune to various antibiotics, often contracted in hospitals, colistin was used.

However, in 2015, it was discovered that there are bacteria that developed resistance to colistin in China. This happened because the medicine has been given to pigs for years, in a preventive way, to prevent the animals from getting sick.

However, the bacteria in these animals developed resistance to the drug and spread to humans.

Side effects

There are many different types of antibiotics and their side effects are varied. The most common, however, involve the bacteria that are killed. Beneficial bacteria that live in the vagina and intestine can be affected by the drug.

Soft stools, diarrhea and nausea are common side effects.


Using antibiotics during pregnancy should be avoided. Some of the stronger ones can cause malformation of the fetus. The doctor must be informed of any infection that affects the pregnant woman in order to indicate the ideal treatment.


There is a possibility that the patient may be allergic to the antibiotic. In this case, the treatment must be stopped immediately and it is necessary to see a doctor for the change of medication to be carried out. It is important that this exchange is made as soon as possible.

The main symptoms of antibiotic allergy are skin rashes , shortness of breath  and swelling in the mouth and tongue .

Other effects

With the variety of antibiotics, several side effects can arise. Between them:

  • Hearing loss;
  • Vertigo;
  • Kidney injury, stones or insufficiency;
  • Brain injury;
  • Decrease in the number of white blood cells;
  • Sensitivity to light (photophobia);
  • Pigmentation of teeth;
  • Eye injury;
  • Temporarily low blood pressure;
  • Convulsions;
  • Liver damage;
  • Headache;
  • Metallic flavor in the mouth;
  • Change in urine color;
  • Diarrhea.
  • Nausea.

Antibiotic is fattening?

No!  Antibiotics are not fattening. What happens is that some antibiotics can cause excess gas during treatment, which can give the feeling and appearance of a swollen belly. This is transient and as soon as the treatment is completed, the excess gas will also go away.

Drug interactions

Antibiotics are several different medications and each of them has varied and specific drug interactions. For example, carbamazepine, a medicine used to treat epilepsy , has a reduced effect when using antibiotics.

It is important to inform the doctor of any medication that is being used during antibiotic treatment, so that he can adjust the dose or choose a type of antibiotic that does not interact with his medication.


For a long time, there was a fear that antibiotics would reduce the effect of contraceptives. There was a theory that the effect of some antibiotics on gut bacteria reduced the absorption and concentration of the pill’s hormone in the woman’s body. The theory made sense, but studies were not done to discover its validity.

However, in recent decades, the problem has been investigated. Studies have shown that an  antibiotic is capable of reducing the effectiveness of the birth control pill: rifampicin , a drug used to treat tuberculosis.

Several other antibiotics have been tested in several studies and none has made a difference in the pill’s effect. Therefore, the use of antibiotics by women taking oral contraceptives – including the morning-after pill – is safe.

If the woman needs to take rifampicin, it is recommended to use other contraceptive methods, such as a condom  or an IUD .

Some doctors may even recommend, for safety, that a woman use a condom or another method during treatment with antibiotics. There is no problem in following this advice.

How and when to use correctly

Antibiotics were a revolution in modern medicine, but today they are used without the necessary care. In Brazil, since 2010, there are laws that limit the indiscriminate purchase of antibiotics. For the sale of the drug, it is necessary to present a prescription in two copies, one of which stays with the pharmacy.

Using the medicine correctly helps to prevent the creation of resistance and superbugs, in addition to making the cure of the disease more guaranteed for the patient.

When to use?

The use of antibiotics should be a last resort. If you are feeling sick, go to the doctor to find out what the disease is and don’t assume it is a bacterium.

Many diseases are caused by viruses, fungi, protozoa and parasites, and antibiotics do not work against these pathological agents. Taking the medicine will only affect the other bacteria in your body, the ones that are not causing any problems, and will create resistance in them.

You should only use antibiotics when the doctor prescribes, since he has the knowledge of which antibiotic can be used for which bacteria, and he is also the one who knows the dose, times and treatment time.

Always respect doses and schedules

Each antibiotic has its specific times and doses to take effect and eliminate bacteria effectively. If you allow the concentration of medication in the body to become too low, the bacteria may have a chance to reproduce again.

However, you should not take more than the dose prescribed by the doctor, as this can have unwanted and dangerous side effects.

What if I forget?

If you miss a dose, take the medicine as soon as you can and remember. Keep the spacing between doses.

If you needed to take a dose every 8 hours, but you forgot one and only remembered four hours later, take a dose as soon as you remember and the next dose should be taken 8 hours later.

I got better, what now?

Continue taking the medication  until the end  of treatment . It is extremely important that you do not stop taking the antibiotic when the symptoms go away. When their numbers drop, the bacteria stop causing symptoms, but several of them are still present.

If you stop using the antibiotic, the chances of them reproducing are high, and worse, they can develop resistance to the drug since only the strongest survived to that point.

Often, the number of doses of an antibiotic treatment matches the number of doses in the medicine boxes, and reaching the end of the box is necessary.

What to do with leftovers?

It is possible that antibiotic doses will be left over at the end of treatment. They must be discarded . Storing antibiotics for later use can facilitate the creation of resistant bacteria, since the amount left over should not be enough for a treatment.

It is important that the disposal is done correctly. Throwing antibiotics into the sewer through the toilet or common trash can expose bacteria from these places to the drug, which can also cause resistance that can spread.

Several pharmacies, in addition to health centers, receive expired medicines and leftover treatment for proper disposal.

You can search for disposal points in your city by clicking here .

Drink a lot of water

Drinking water helps the liver to filter the blood more easily, eliminating both dead bacteria and remnants of the drug. It is recommended to drink around 2 liters of water per day.