Beta-lactam antibiotic: mechanism of action and classification

Antibiotics - a group of drugs that have an etiotropic mechanism of action. In other words, these medicines act directly on the cause of the disease (in this case, the pathogen) and do this in two ways: they destroy microbes (bactericidal drugs - penicillins, cephalosporins) or prevent their reproduction (bacteriostatic - tetracyclines, sulfonamides).

There is a huge number of medicines that are antibiotics, but the most extensive group among them is beta-lactams. It is about them that will be discussed in this article.

Classification of antibacterial agents

On the mechanism of action, these drugs are divided into six main groups:

1. Antibiotics that disrupt the synthesis of components of cell membranes: penicillins, cephalosporins, etc.
2. Medicines that interfere with the normal functioning of the cell wall: polyenes, polymyxins.
3. Preparations, suppressing the synthesis of proteins: macrolides, tetracyclines, aminoglycosides, etc.
4. Suppressive synthesis of RNA during the action of RNA polymerase: rifampicins, sulfonamides.
5. Suppressive synthesis of RNA during the action of DNA polymerase: actinomycins, etc.
6. DNA synthesis blockers: anthracyclines, nitrofurans, etc.

However, this classification is not very convenient. In clinical practice, the following division of antibacterial drugs was adopted:

1. Penicillins.
2. Cephalosporins.
3. Macrolides.
4. Aminoglycosides.
5. Polymyxins and polyenes.
6. Tetracyclines.
7. Sulfonamides.
8. Derivatives of aminoquinolones.
9. Nitrofurans.
10. Fluoroquinolones.

Beta-lactam antibiotics. Structure and mechanism of action

This is a group of drugs with a bactericidal effect and a fairly wide list of indications for use. To beta-lactam antibiotics include penicillins, cephalosporins, carbapenems, monobactams. All of them are characterized by high efficiency and relatively low toxicity, which makes them the drugs most often prescribed for the treatment of many diseases.

The mechanism of action of beta-lactam antibiotics is due to their structure. Excessive details here to anything, it is necessary to mention only the most important element, which gave the name to the entire group of drugs. The beta-lactam ring, which is part of their molecules, provides a pronounced bactericidal effect, which manifests itself by blocking the synthesis of elements of the cell wall of the pathogen. However, many bacteria are able to produce a special enzyme that breaks the structure of the ring, thereby depriving the antibiotic of its main weapon. That is why the use of drugs that do not have protection against beta-lactamases in treatment is ineffective.

Antibiotics of the beta-lactam group, protected from the action of the bacterial enzyme, are becoming increasingly common. They include substances that block the synthesis of beta-lactamases, for example, clavulonic acid. This is how protected beta-lactam antibiotics (such as "Amoxiclav") are created. Other inhibitors of the bacterial enzyme include Sulbactam and Tazobactam.

Drugs from the Penicillin Group: A Historical Reference

Preparations of this series were the first antibiotics, the therapeutic effect of which became known to people. For a long time they were widely used to treat various diseases and in the first years of use were almost a panacea. However, very soon it became clear that their effectiveness was gradually decreasing, as the evolution of the world of bacteria does not stand still. Microorganisms are able to quickly adapt to a variety of complex conditions of existence, giving birth to generations of antibiotic-resistant bacteria.

The prevalence of penicillins has led to the rapid growth of insensitive strains of microbes, so in its pure form preparations of this group are now ineffective and hardly applied. They are best used in combination with substances that enhance their bactericidal effect, as well as suppressing the protective mechanisms of bacteria.

Penicillin preparations

These are beta-lactam antibiotics, the classification of which is quite extensive:

1. Natural penicillins (for example, "Benzylpenicillin").
2. Antistaphylococcal ("Oxacillin").
3. Penicillins of the extended spectrum of action ("Ampicillin", "Amoxicillin").
4. Anti-synergic ("Azlocillin").
5. Protected penicillins (combined with clavulonic acid, "Sulbactam", "Tazobactam").
6. Preparations that include several antibiotics of the penicillin series.

Overview of drugs belonging to the group of penicillins

Natural penicillins can successfully suppress the activity of both gram-positive and gram-negative microorganisms. Of the latter, streptococci and the causative agent of meningitis are the most sensitive to this group of beta-lactam antibiotics . Other bacteria have by now acquired protection mechanisms. Natural penicillins are effective against anaerobes: clostridia, peptococci, peptostreptococcus, etc. These drugs are the least toxic and have a relatively small number of undesirable effects, the list of which reduces mainly to allergic manifestations, although overdose may lead to the development of convulsive syndrome, and the appearance of symptoms of poisoning with Side of the digestive system.

Of the antistaphylococcal penicillins, the most important is a beta-lactam antibiotic, such as "Oxacillin." This drug is for narrow use, since it is intended primarily for the control of Staphylococcus aureus. It is against this pathogen (including penicillin-resistant strains) that "Oxacillin" is most effective. Side effect is similar to that of other representatives of this group of drugs.

Penicillins of the extended spectrum of action in addition to gram-positive, gram-negative flora and anaerobes are also active against intestinal pathogens. Side effects do not differ from the above, although these drugs are characterized by a slightly higher probability of disorders from the digestive system.

Beta-lactam antibiotic "Azlocillin" (a representative of the fourth group of penicillins) is designed to fight with Pseudomonas aeruginosa. However, at present, this pathogen has shown resistance to the drugs of this series, which makes their use not so effective.

Protected penicillins have already been mentioned above. Due to the fact that these drugs include substances that inhibit beta-lactamase bacteria, they are more effective in treating many diseases.

The latter group is a combination of several representatives of the penicillin series, mutually reinforcing the effect of each other.

Four generations of bacteria fighters

Beta-lactam antibiotics are also cephalosporins. These drugs, like penicillins, are characterized by a broad spectrum of action and insignificant side effects.

There are four groups (generations) of cephalosporins:

1. The brightest representatives of the first generation are "Cefazolin" and "Cephalexin". They are designed primarily to combat staphylococci, streptococci, meningococci and gonococci, as well as some gram-negative microorganisms.
2. The second generation is the beta-lactam antibiotic "Cefuroxime". Its area of responsibility includes mainly gram-negative microflora.
3. "Cefotaxime", "Ceftazidim" - representatives of the third group of this classification. They are very effective against enterobacteria, and are also capable of destroying the nosocomial flora (hospital strains of microorganisms).
4. The main product of the fourth generation is Cefepime. It has all the advantages of the above medicines, in addition, it is extremely resistant to the action of beta-lactamase bacteria and has activity against Pseudomonas aeruginosa.

Cephalosporins and beta-lactam antibiotics generally have a pronounced bactericidal effect.

Of undesirable reactions to the introduction of these drugs, the most attention deserves a variety of allergic reactions (from minor rashes to life-threatening conditions, such as, for example, anaphylactic shock), in some cases, disorders of the digestive system.

Reserve facility

"Imipenem" is a beta-lactam antibiotic belonging to the carbapenem group. He, as well as no less famous "Meropenem", on the effectiveness of exposure to drug-resistant microflora can give odds to the third and fourth generations of cephalosporins.

Beta-lactam antibiotic from the group of carbapenems is a drug used in especially severe cases of diseases, when pathogens are not amenable to treatment with other drugs.

Reserve facility number two

"Azrethonam" is the most vivid representative of monobactams, it is characterized by a rather narrow spectrum of action. This beta-lactam antibiotic is most effective against gram-negative aerobes. However, it should be noted that, like Imipenem, Aztreon is practically insensitive to beta-lactamases, which makes it the drug of choice for severe forms of diseases caused by these pathogens, especially when other antibiotics are ineffective.

Spectrum of beta-lactam antibiotics

Summarizing the above, it should be noted that the drugs of these groups have an impact on a huge number of varieties of pathogens. The mechanism of action of beta-lactam antibiotics is such that it leaves no chance for microbes to survive: blockade of cell wall synthesis is a death sentence for bacteria.

Gram-positive and gram-negative organisms, aerobes and anaerobes ... On all these representatives of the pathogenic flora there is a highly effective drug. Of course, there are highly specialized drugs among these antibiotics, but most are still ready to engage in battle with several pathogens of infectious diseases. Beta-lactam antibiotics can resist even the representatives of the nosocomial flora, which is the most resistant to treatment.

What are hospital strains?

It is a question of microorganisms existing in medical institutions. Sources of their appearance are patients and medical staff. Especially dangerous are hidden, sluggish forms of diseases. The hospital is an ideal place where vectors of all possible types of infectious diseases are collected. And violations of sanitary rules and norms are fertile soil for this flora to find a niche for existence, wherever it could live, reproduce and acquire resistance to medicines.

The high resistance of hospital strains is due primarily to the fact that, by choosing a hospital facility as their habitat, the bacteria are able to contact various drugs. Naturally, the effects of drugs on microorganisms occur accidentally, without the goal of destroying, and in small doses, and this contributes to the fact that representatives of hospital microflora can develop protection against harmful mechanisms for them, learn to resist them. So there are strains, it is very difficult to struggle with, and sometimes it seems that it is impossible.

Antibiotics of the beta-lactam series in one way or another try to solve this complex problem. Among them there are representatives who are able to successfully fight even the most bacteria-insensitive to bacteria. These are reserve drugs. Their application is limited, and they are appointed only in the case when it is really necessary. If these antibiotics are used unreasonably often, then, most likely, this will result in a decrease in their effectiveness, because then the bacteria will be able to interact with small doses of these drugs, study them and develop ways of protection.

When are beta-lactam antibiotics prescribed?

Indications for the use of this group of drugs are due primarily to their spectrum of action. It is most expedient to prescribe beta-lactam antibiotic for infection, The causative agent of which is sensitive to the action of this drug.

Penicillins have proven themselves in the treatment of pharyngitis, tonsillitis, pneumonia, scarlet fever, meningitis, bacterial endocarditis, actinomycosis, anaerobic infections, leptospirosis, salmonellosis, shigellosis, infectious diseases of the skin and soft tissues. Do not forget about the drugs that can fight with Pseudomonas aeruginosa.

Cephalosporins have a similar spectrum of action, and therefore the indications for them are almost the same as for penicillins. However, it should be said that the effectiveness of cephalosporins, especially the last two generations, is not an example higher.

Monobactams and carbapenems are designed to fight the most severe and ill-treatable diseases, including those caused by hospital strains. They are also effective for sepsis and septic shock.

Undesirable action

As already mentioned, beta-lactam antibiotics (drugs related to this group are listed above) are characterized by a relatively small amount of harmful effects to the body. Rarely occurring convulsive syndrome and symptoms of digestive system disorders do not pose a threat to life. Really dangerous can be severe allergic reactions to the introduction of drugs from beta-lactam antibiotics.

Rashes, itchy skin, rhinitis and conjunctivitis do not pose a threat to life, although they are very unpleasant. What is really to be feared is severe reactions such as Quincke's edema (especially in the larynx, which is accompanied by severe suffocation, even to the inability to breathe) and anaphylactic shock. Therefore, the drug can be administered only after performing a sample for allergy.

There are also possible cross reactions. Beta-lactam antibiotics, the classification of which implies the presence of a large number of groups of drugs, are very similar in structure to each other, which means that in the case of intolerance of one of them, all the others will also be perceived by the body as an allergen.

A few words about the factors that increase the resistance of bacteria

The gradual decrease in the effectiveness of antibacterial drugs (including beta-lactam antibiotics) is due to the unjustifiably frequent and often misdirected use of antibiotics. Incomplete treatment, the use of small therapeutic doses do not contribute to recovery, but they give microorganisms the opportunity to "train", invent and practice methods of protection from drugs. So is it any wonder that the latter become ineffective over time?

Although now antibiotics are not released in pharmacies without a prescription, you can still get them. This means that self-treatment and related problems (the use of the same drug, unreasonable interruption of therapy, incorrectly selected doses, etc.) will remain, creating conditions for the cultivation of resistant strains.

The hospital flora, which has the opportunity to actively contact with various drugs and to invent new ways of counteracting them, will not disappear anywhere.

What to do? Do not engage in self-medication, follow the recommendations of the doctor in charge: take the medication for as long as required, and in the right doses. With the nosocomial flora, of course, it is more difficult to fight, but it is still possible. Tightening sanitary norms and their strict implementation will reduce the likelihood of creating favorable conditions for the reproduction of resistant flora.

A few words in conclusion

A very extensive topic is beta-lactam antibiotics. Pharmacology (the science of drugs and their effects on the body) devotes a few chapters to them, which include not only a general characteristic of the group, but also contain a description of the most famous of its representatives. The same article does not pretend to be complete, only attempts to acquaint with the main points, which it is absolutely necessary to know about these medicinal products.

Be healthy and do not forget: before using any antibiotic, carefully study the instructions and follow the recommendations, and even better consult a specialist.