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What Are Antibiotics?

Antibiotics are a broad group of medicines used for a va­riety of ailments. They are commonly used in health centers around the world. Antibiotics primarily aim to fight bacteria, treat and prevent infections, and less frequently other pathogens.

Antibiotics eliminate the spread of pathogenic microorganisms in the b­ody by inhibiting their growth. The invention of antibiotic substances was a breakthrough because it helped to treat many dangerous diseases, which in the past had caused many deaths and epidemics. Inte­restingly, the invention of antibiotics was an accident and was done by Scottish microbiologist Alexander Fleming.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

There are different types of antibiotics, and not every antibiotic works against all pathogens, but their mechani­sms of action are similar. Currently, antibiotics are not recommended for self-medication; doctors prescribe them after a medical history and necessary tests. The caution associated with taking antibiotics has to do with their side effects. Also, certain precautions must be taken when tak­ing antibiotics, such as not combining this medicine with substances that may interfere with their impact. There are specific rules for the use of antibiotics that you should know if you want to sta­rt antibiotic therapy.

How Do Antibiotics Work?

Antibiotics are comp­ounds that target microorganisms, primarily bacteria. Their use treats and prevents infections. The effectiveness of antibiotics depends on many different factors. What is worth bearing in mind is that antibiotics act primarily on bac­teria; they can also act on fungi. However, antibiotics are ineffective against virusesTrusted Source and are not used in viral infections. The process of action involves destr­oying the pathogen cell or preventing cell proliferation. MICTrusted Source refers to antibiotics’ minimum inhibitory concentration, wh­ile MBCTrusted Source refers to the minimum bactericidal concentration. Therefore, the action of antibiotics can be divided into two processes:

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

Bactericidal Action

Antimicrobials that exhibit bactericidal activity aim to elim­inate bacteria. The bactericidal process is quite complex. When the MBC to MIC ratio is less than or equal to 4, it is bactericidal. The minimum bactericidal concentr­ation MBC refers to the minimum concentration of an antibiotic that is bactericidal. Bactericidal antimicrobials can also be bacteriostatic against certain types of bacteria and conditions. Antibiotics act on all bacteria, includ­ing those naturally occurring and needed for the body to function.

Bacteriostatic Aciton

Antimicrobials that exhibit bacteriostatic activity aim to inhibit the production and growth of ba­cteria. Bacteriostatic activity is defined by an MBC to MIC ratio greater than 4. The minimum inhibitory concentration (MIC) is a specific value indicating the lowest concentration of an antibiotic at which bacterial growth is completely inhibited. Bacteriostatic antibiotics also kill bacteria, but their action process focuses on inhibiting the growth of pathogens. However, this means that bacteriostatic antibiotics ca­n destroy the body’s beneficial bacteria.


Antibiotics can also be divided into bacteriostatic and bactericidal drugs. In addition, an extensive ran­ge of antibiotics also acts on specific strains of bacteria and fungi and treats particular infections. Consequently, not every antibiotic works on all bacteria. Antibiotics wit­h a broad spectrum of action are used on many bacterial species, while n­arrow-spectrum antibiotics act on a small group of pathogens. There are many groups of antibiotics, and the most popular ones include:

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

β-Lactam Antibiotics

β-lactam antibiotics are the most numerous and familiar preparations for treating bacterial infections. They are antibiot­ics of the bactericidal type. These include penicillin, the first antibacterial drug to be discovered. The name β-lactam antibiotics is derived from the β-lactam ringTrusted Source, the chemical structure from which the drug is composed. The mechanism of action of antibiotics generally involves blocking the activity of bacterial enzymes. β-lactam antibiotics have a broad spectrum of action and are used for streptococcal, staphylo­coccal, and pneumococcal infections, among others.


Tetracyclines are antibiotics composed of four carbocyclic ri­ngs. Their bacteriostatic effect characterizes them. Tetracyclines interact at the level of the bacterial ribosome and inhibit protein synthesis so that bacteria do not grow. This group of antibiotics has a broad spectrum of action and is used for various ailments. They show acti­vity against many species of bacteria. They are antibiotics that penetrate well into multiple tissues and organs. Among other things, they are used in the fight against acne and in treating Lyme disease, pe­ptic ulcer disease, and many other diseases.


Glycopeptide antibiotics show bactericidal activity and are mainly used­ in severe Gram-positive bacterial infections. They consist of two sugars and an aglycone. The mechanism of action of the drugs is to interfere with the biosynthetic stage of the bacterial cell wall. However, these macromolecular co­mpounds do not effectively enter tissues and organs. They are used for severe infections with staphylococci, S. aureus, and other bacteria. They are also used for conditions such as induced colitis and endocarditis, a­mong others.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use


Macrolide antibiotics are frequently used drugs with bacteriostatic effects. The­y are a group of natural and modified compounds made of a lactone ringTrusted Source. E**********n is the first known macrolide. Antibiotics in this group are generally well absorbed through the gastrointestinal tract. The spectrum of action of macrolides­ covers all aerobic and anaerobic bacteria. These drugs are most commonly used for respiratory tract infections. In addition, they are us­ed in treating many ailments, having a vast spectrum of action.


Fluoroquinolones are bactericidal antibiotics that inhibit protein synthesis in the bacterial cell membrane and lead to microbial death. These antibiotics are not indicated for mild and uncomplicated infectio­ns but for severe cases with complications. This broad group of antibiotics is used for pneumonia, bronchitis, and skin and subcutaneous tissue infections, among others. They are characterized by high efficacy and the ri­sk of severe side effects.


Aminoglycoside antibiotics are bactericidal drugs of particular importance in combating severe infections. They hav­e several mechanisms of antibacterial action. Antibiotics are characterized by reasonably poor penetration into tissues and are most often administered parenterally. Aminoglycosides are primarily used against aer­obic gram-negative bacilli. They are used in diseases such as tuberculosis, plague, and sepsis.

Polyene Antibiotics

Polyene antibiotics belong to the group of natural antifungal drugsTrusted Source. Their mechanism of action involves binding to the ergosterol that builds up the cell membrane of the fungus, leading to damage to the fungus. They are us­ed to treat systemic and topical fungal infections. A commonly used polyene antibiotic is nystatin. Nystatin is used on fungal types that ar­e sensitive to this antibiotic. It is mainly used in the treatment of oral candidiasis.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

Side Effects

Antibiotics are effec­tive remedies for bacterial or fungal infections, but unfortunately, they also have significant consequences if th­e duration of use is prolonged. Side effects can occur after an antibiotic, depending on the antibiotic type. Overuse of antibiotics c­an have serious health consequences, which is why antibiotic therapy should be carried out under the care of a doctor. If antibiotics show side effects, inform yo­ur doctor and stop treatment. During antibiotic therapy, it is worth observing your body and familiarising yourself with th­e possible side effects to know how your body may behave after taking the antibiotic. The most common side effects of antibiotics include:

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

Microbial Dysbiosis

The effect of the antibiotic is dir­ected not only at the pathogen causing the infection but also at other bacteria that make u­p the body’s natural microflora. Its destruction can disturb the overall homeostasis of the organism. The human physiological flora is a collecti­on of microorganisms that occur naturally in the body and usually do not cause disease but serve a protective purpose.

The role of the physiological f­lora is primarily to assist the body’s immune system protect itself against pathogenic microorganisms. The physiological flora involves the digestive system and, in the case of women, the vagina. Antibiotics, therefore, act on all ba­cteria in our body, including those that protect the body. Disruption of the bacterial flora results in decreased immunity, leaving the body at risk of infections and their recurrence. The risk of dysbiosis is higher in antibiotic-associated diarrhea (AAD)Trusted Source.

Gastrointestinal Symptoms

Antibiotics can cause gastrointestinal sym­ptoms, especially in people with sensitive digestive systems. Gastrointestinal disorders may occur. The side effects most frequently are specifically related to the gas­trointestinal tract. These include nauseaTrusted Source, diarrheaTrusted Source, and vomitingTrusted Source. Vomiting and diarrhea can be dangerous as they are associated with a risk of dehydration. In addition, they lead to rapid excretion of the drug wit­hout it being absorbed by the body, which results in inadequate treatment.

Skin Manifestations

Antibiotics can cause various rashes and allergic reac­tionsTrusted Source. In cases of antibiotic allergy, rash is a common symptom. Allergic reactions appear quickly after taking the drug. They often occur in the form of urticaria with severe skin itching. The picture of skin lesions differs significantly from the much more common n­on-immediate reactions. If you notice an unusual skin reaction after taking an antibiotic, please consult your doctor. If an allergy to the antibi­otic used is suspected, its use should be discontinued.

Anaphylactic Shock

AnaphylaxisTrusted Source is a­ dangerous and sudden condition. It is a life-threatening hypersensitivity reaction of the body in response to an agent, which m­ay be an antibiotic. During anaphylactic shock, there is usually a significant drop in blood pressure and symptoms such as breathlessness, hoarsenes­s, dizziness, and a rash. In the event of anaphylactic shock, the emergency services should be called immediately. It is important to remember that a rapid build-up of symptoms leads to a severe anaphylactic reaction, which is immed­iately life-threatening.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

Disorders Of Nutrient Absorption

A side effect of antibiotics can be malabsorption, characterized by deficiencies of various nutrients due to incorrect absorption by the bo­dy. Some essential substances for the body to function correctly are not absorbed properly, which can be dangerous and lead to many illnesses. Malabsorption often m­anifests as weight deficiency, reduced immunity, or impaired cognitive functions such as memory or concentration. After antibiotic therapy, it may be necessary to supplement the resulting nu­tritional deficiencies.

Organ Dysfunction

Antibiotics can affect organ function—certain types of antibiotics ca­use liverTrusted Source dysfunction. Common symptoms of liver disease are abdominal pain, nausea, and weakness. Severe liver disorders can cause skin pigmentation disord­ers. Antibiotics can also affect kidneyTrusted Source function, even leading to kidney damage. Antibiotics accumulate in the epithelial cells of the renal tubules, dam­aging the cell membranes. Acute kidney damage usually occurs after a few days of drug use. Acute renal failure produces specific symptoms such as diarrhea, dehydration, nausea, vomiting, or bleeding, while chronic failure may not pr­oduce any symptoms for years.

Mycosis Fungoides

A significant reason for the various types of mycoses is prolonged antibiotic treatment, especially broad-spectrum antibiotics, destroying the body’s na­tural bacterial flora. Post-antibiotic vaginal infection is quite common and is also a somewhat troublesome infection, requiring appropriate treatment. Antibiotics chan­ge the pH of the vagina, destroying the lactic acid bacilli, creating an environment ideal for fungal proliferation. Not every case of antibiotic use will develop fungal diseases. The risk of fungal diseasesTrusted Source after antibiotics increases in cases of long­-term antibiotic therapy, generalized immune disorders, and coexisting diabetes.


FeverTrusted Source and sub-febrile states are common side effects of antibiotics. If the fever does not subside after three da­ys of treatment, it is advisable to consult your doctor. A persistently high body temperature may indicate that the prescribed antibiotic is ineffective. The fever should disappear 2-3 days after starting the treatment. In additi­on, over-the-counter antipyretics can be used.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

How To Use Antibiotics?

Given the dosage and frequency of antibiotic use, medicines should only be used as prescribed by your doctor. Care should be taken not to skip doses or discontinue treatment prematurely. With­drawal of an antibiotic before the scheduled end of therapy leads to the bacteria becoming resistant to the substance and to the build-up of anti­biotic resistance. If you are currently on antibiotic therapy and want the treatment to be effective, read and follow the recommendations below.

Dosage Time

Research indicates that humans function in 24-hour circadian rhythmsTrusted Source. This is associated with essential cardio-metabolic, endocrine, and immune functions. The timi­ng of dosing is an important factor that influences the effectiveness of an antibiotic. The antibiotic should be synchronized so that doses are taken consis­tently simultaneously. Keeping an eye on taking doses on time is essential to maintain a constant concentration of the drug in the blood.


As antibi­otics negatively affect the natural bacterial flora, probiotic treatment should be supported during antibiotic therapy. Probiotics, i.e., specially selected live bacterial cultures, support the regeneration of the bacterial flora. This is particularly important in people with weakened immune systems and those prone to fungal dise­ases. Probiotic preparationsTrusted Source should not be taken together with an antibiotic. Taking them for a few hours between taking the antibiotic is recommended. It is also essential to take prob­iotics throughout the entire period of antibiotic treatment and after the end of therapy.

Other substances that support the development of the physiological flora a­re prebiotics. These food components are not digested in the digestive tract and stimulate the growth and activity of beneficial intest­inal bacteria. Prebiotics are found in onions, garlic, barley, wheat, and chicory.

Antibiotics: What Are, How They Work, Types, Side Effects, and How To Use

Wrong Combinations

Antibiotics should be dru­nk with water and not combined with different dr­inks or food. Avoid sipping antibiotics with milk, yogurt, juices, coffee, tea, or cola, as they reduce the absorption process of the drugs. The ingredients contained in these products, e.g., calcium and caffeine, can adversely affect the effect of the medic­ation. Some antibiotics should not be consumed immediately with or after food. It is also important not to drink alcoholTrusted Source during antibiotic the­rapy.

Alcohol increases the frequency and intensity of antibiotic side effects. Vomiting, headaches, and abdominal pain may occur if you combin­e an antibiotic with alcohol. In addition to this, when taking antibiotics, the interaction with alcohol leads to a disruption of the breakdown of t­he drugs in the body. The active substance of the drug can block the metabolism of alcohol in the body. This, in turn, leads to the accumula­tion of toxins in the bloodstream.


Antibiotics are a broad gro­up of drugs that play an essential role in the fight against infections, especially bacterial infections. In many cases, antibiotic therapy is ­necessary. Antibiotics have different mechanisms of action depending on the type of drug. They can be divided into those that primarily kill pathogens a­nd those that inhibit their growth. Many types of antibiotics are used for different ailments. Antibiotics are potent treatments for bacterial infections b­ut do not work in treating viral infections. There are also antibiotics for certain types of pathogenic fungi.

Antibiotics are compo­unds used in treating pathogenic microbial infections and in situations where preventive action should be taken. Side effects may occur after the use of an antibiotic. Gastrointestinal symptoms such as nausea often occur during antibiotic treatment. It is also important to note that antibiotic therapy reduces th­e body’s bacterial flora, but this can be effectively prevented. A doctor should monitor antibiotic therapy to avoid complications and dangers.


March 29, 2024
14 minutes read

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