Antibiotics belong to a class of drugs that is very important to society as a whole. Without these drugs there would be many more deaths and many surgeries would be impossible to perform because of the risk of postoperative infection, as in heart transplantation.

Unfortunately, in recent years, more and more cases of antibiotic resistance have been observed. In other words, in the past certain antibiotics allowed the treatment of many infectious diseases, now we see some people dying from simple infections (often acquired in hospitals) because the antibiotic is no longer effective.

In the United States alone (about 5% of the world’s population), the CDC (state health agency) estimates that 23,000 is the number of deaths of people infected with antibiotic-resistant microorganisms.

It is estimated that 50% of antibiotic prescriptions in humans (also remember that many antibiotics are used in animals) are unnecessary. Create has already mentioned that, in case of sore throat and sinusitis , for example, if the cause is viral, antibiotics are useless.

You should know that many deaths, even today, are caused by bacteria. For example, most flu deaths are not caused by the virus itself, but by a bacterial infection causing pneumonia, for example. In these cases, antibiotics can save the patient’s life.

It is the most prescribed class of drugs in the world.

In Brazil, 40% of all drugs sold in pharmacies are antibiotics [source: Folha de São Paulo, June 18, 2010].


The word antibiotic, in the etymological sense means: against (anti) living organisms (biotic). The word biotic means more precisely: against bacteria. Antibiotics can be of natural or synthetic origin.


Discovery of penicillin
In 1928, Dr Alexander Fleming was the first to discover an antibiotic: the Penicillium fungus. This substance prevents the development of certain bacteria in cultures. This great discovery, one of the most important of the 20th century, made possible a few years later (1940), the development of the antibiotic penicillin (penicillin G) which helped and continues to save millions of lives. This also paved the way for research and development of new classes of antibiotics against tuberculosis, pneumonia, skin infections. etc.

classes of antibiotics

In the table below you can find some information about the classification of antibiotics (antibiotic class).

There may be different classifications, but we believe that the one based in part on the chemical structure of the antibiotic and on the effect on the bacterial region may be interesting for patients and professionals (doctors, pharmacists, nurses,…).

class of antibioticsMain molecules – active principles of the familyIndications (eg in general)Main side effects*Action on bacteria (form of action)Galenic forms of the drug (in general)
Penicillins (beta-lactamase)
Amoxicillin + ev. a lactamase inhibitor= clavulanic acidMiscellaneous ( bronchitis , pneumonia , ENT, meningitis ,…)Diarrhoea, allergy (up to 5% of the diseases treated), digestive and renal toxicity,…Bacterial wall synthesis inhibitors (bactericidal action)– per os, injectable, local
Penicillin G. Original penicillin substance!
Penicillin V
Cephalosporins (beta-lactamase)
1st generation
– Cefaclor
– Cefazolin
Miscellaneous ( bronchitis , pneumonia , ENT, meningitis ,…)Allergy, kidney toxicity (high dose)Bacterial wall synthesis inhibitors (bactericidal action)– per os, injectable
2nd generation
– Cefamandole
– Cefuroxime
Allergic reactions, bleeding
3rd generation
– Cefixime
– Cefpodoxime
– Cefotaxime
– Ceftazidime
– Ceftriaxone
antibiotic familyMain molecules – active principles of the familyIndications (eg in general)Main side effects*Action on bacteria (form of action)Galenic forms of the drug (in general)
Aminosides (Aminoglycosides)
StreptomycinTuberculosisToxicity in the auditory region (otoxicity) and renal (nephrotoxicity, usually reversible)Protein synthesis inhibitors (bactericidal function)– per os, injectable, local
NeomycinSensitive germs, e.g. infectious eye diseases, intestinal diseases, infected wounds, serious illnesses




ENT, genital infections,…Allergy, digestive toxicity, liver toxicityProtein synthesis inhibitors (bactericidal function)– per os, injectable, local
antibiotic familyMain molecules – active principles of the familyIndications (eg in general)Main side effects*Action on bacteria (form of action)Galenic forms of the drug (in general)
Acne, genital infections, lung infections,…Allergy, digestive toxicity, kidney toxicity, in the neuronal region,….Protein synthesis inhibitors (bactericidal function)– per os, injectable, local
(Fluoro) quinolones (=gyrase inhibitor)
Urinary infections ( cystitis ), genital infections,…Allergic reaction, auditory toxicity, tendinitis,…bacterial gyrase inhibitor– per os, injectable
antibiotic familyMain molecules – active principles of the familyIndications (eg in general)Main side effects*Action on bacteria (form of action)Galenic forms of the drug (in general)
sulfamethoxazol e trimetoprima=co-trimoxazol
In case of failure with other antibiotics when there is genital urinary infections, Crohn’s disease (sulfazalazine) …Allergy, blood toxicity, kidney,…Tetrahydrofolic acid synthesis inhibitors– per os, injectable, local
Other (miscellaneous)
– Fosfomycin
– Clindamycin
– Thiamphenicol
– Imipenem
– Metronidazole
– Vancomycin
Variable ( cystitis , acne , genital infections,…)Miscellaneous, depending on the antibioticseveral– per os, injectable, local
Isoniazid Pyrazinamide
Rifampin Streptomycin
TuberculosisSeveralSeveral– orally (via orally)

Antibiotic resistance

Antibiotic resistance (or antibiotic resistance) is when a bacterium becomes insensitive to one or several antibiotics. We can say that the bacteria found a way to fight its aggressor (the antibiotic) by different mechanisms, such as the synthesis of the enzyme (beta-lactamase) that will try to render the antibiotic inactive.


What is troubling about resistance to an antibiotic is that the drug was active and effective in destroying bacteria, but over time it has had less or no effect. It is a serious risk to all of humanity.

To qualify these resistant bacteria, we also call them super-resistant bacteria (super-bugs in English). These are bacteria that no longer respond to conventional antibiotics, generally broad-spectrum, with few side effects and frequently used. The doctor will then choose antibiotics that are more specific or that cause more side effects, sometimes serious for the patient. In some cases, the antibiotic is simply ineffective and can cause the patient’s death.

Some scientists believe that we have entered or are at risk of entering a “pre-antibiotic” and “post-antibiotic” era (depending on the reference time). In other words, we see some people die before our eyes, because no antibiotic is effective, as it was before the advent of antibiotics. For example, the 1918 flu epidemic caused tens of thousands of deaths, mainly due to the lack of antibiotics. In fact, most patients do not die from the flu virus, but as a result of bacterial infections that affect the lungs (bacterial pneumonia).

Deaths in the United States (Antibiotic Resistance)
In the United States, about 35,000 people die from antibiotic-resistant bacteria each year. There are a total of 2.8 million infections caused by pathogens that cannot be killed even with modern antibiotics, according to a statement from the US health authority CDC, published on November 13, 2019. The most dangerous intestinal bacteria Clostridioides difficile is responsible for 12,800 of these deaths.

You should know that in some countries it is possible to buy antibiotics without a prescription and there is also the use of antibiotics in animals, these two facts combined can explain the increase in bacterial resistance to antibiotics.

We can explain the increase in resistance to antibiotics by abusive use (for example, in the case of viral diseases, which is useless), in excess or inappropriately (dosage and treatment not followed until the end). We must also take into account the intelligence of nature (in the case of bacteria).

However, as well as for ecology and its problems, man can strongly contribute to the reduction of resistance to antibiotics by reducing their inappropriate use. In France, an advertising campaign with the following slogan: “Les antibiotiques c’est pas automatique!” (antibiotics are not automatic), seems to have had a positive effect in reducing the consumption of antibiotics in recent years.

The main antibiotic-resistant bacteria (according to a WHO report published in late April 2014):

– Escherichia coli: cause urinary infections, such as cystitis

– Klebsiella pneumoniae: provoca pneumonia

– Staphylococcus aureus: causes bloodstream infections

– Streptococcus pneumoniae: cause pneumonia from the ear

– Non-typhoidal Salmonella: causes diarrhea

– Shigella: causes diarrhea

– Neisseria gonorrhea: causes gonorrhea (see above)

Side effects, contraindications and interactions

Side effects, contraindications and interactions depend on the antibiotic class and even the molecule itself. Below you will find in summary the main undesirable effects that may occur:

Side effects of antibiotics (in general)
The main side effects of antibiotics are: complications in the gastrointestinal region, such as diarrhea, vaginal mycoses caused by Candida albicans and allergies.
Some antibiotics can also trigger sun rashes. To find out all the side effects of an antibiotic, read the package insert and ask a specialist for advice.

Antibiotic contraindications (in general)
Allergy to the antibiotic. It is estimated that about 5% of the population is allergic to penicillin. To find out all the side effects of an antibiotic, read the package insert and ask a specialist for advice.

Interactions with antibiotics (in general)
Any antibiotic can have interactions, but take special care with the pill (certain antibiotics can reduce its effectiveness and therefore contraception ends up not being 100%).

An interesting example of interaction occurs, for example, with doxycycline and the use of Rennie® (based on calcium carbonate and magnesium carbonate, against gastric hyperacidity). The use of Rennie® inactivates doxycycline, so do not take Rennie® if you are using a doxycycline-based treatment.

Another example is the interaction between antibiotics and N-acetylcysteine ​​(used to treat cough).

What to do? To use N-acetylcysteine ​​and different antibiotics such as amoxicillins, penicillins, tetracyclines, cephalosporins, aminoglycosides, macrolides and amphotericins: respect an interval of 2 hours between N-acetylcysteine ​​and the antibiotic.


Here are some practical tips your doctor can give you when prescribing antibiotics.

– Respect the dosage prescribed by the doctor (take the exact number of pills, respect the times and whether it should be taken on an empty stomach or not…). For example, if the doctor prescribes antibiotics twice a day (morning and evening) for 10 days (box of 20 pills), respect the indication, otherwise you will be contributing to antibiotic resistance.

– If you are allergic to a class of antibiotics (eg penicillin or its derivatives), tell your doctor, as an allergy is always stronger after the second use. You will need to find an alternative to this class of antibiotics.

– Avoid drinking milk with the antibiotic, as this can reduce the good absorption of the medicine.

– Also avoid alcohol consumption, as this can often reduce the effectiveness of the antibiotic. In any case, alcohol is never advised for the sick, as it does not help with healing.

– If you are pregnant, ask your doctor if you can take an antibiotic (do not self-medicate). It is important to know that some antibiotics should not be taken during pregnancy.
A study published in 2017 in the British Journal of Clinical Pharmacologyand carried out in Quebec (Canada) showed that certain antibiotics taken during pregnancy can lead to congenital malformation. According to the study, clindamycin, doxycycline, quinolones, macrolides and phenoxymethylpenicillin were linked to malformations in certain specific organs. Amoxicillin, cephalosporin and nitrofurantoin were not associated with congenital malformations. This study focused on the analysis of 139,938 births in Quebec (Canada) between 1998 and 2008. Canadian scientists believe that it is important to give preference to safe antibiotics during pregnancy in case of infections such as cystitis, especially in the first trimester.

– Antibiotics often cause diarrhea as a side effect. To limit digestive problems. You can eat yogurt (rich in lactic acid bacteria to rebuild the intestinal flora, partly destroyed by antibiotics) or buy preparations based on lactic acid bacteria (eg Bioflorin®) at the pharmacy.

– Ask a pharmacist for advice if you are taking other medications, to limit interactions. Interactions may occur with the contraceptive pill (decreased effectiveness) and certain antacids (inactivation of the antibiotic, doxyclin).

Jeanne Kenney
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I’m a stylist trainer, a content creator, and an entrepreneur passion. Virgo sign and Pisces ascendant, I move easily between my dreams, the crazy world I want, and my feet on the ground to carry out my projects.

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