Antibiotics are a group of drugs with an etiotropic mechanism of action. In other words, these medicines act directly on the cause of the disease (in this case, the causative microorganism) and do this in two ways: they destroy microbes (bactericidal drugs - penicillins, cephalosporins) or prevent their reproduction (bacteriostatic - tetracyclines, sulfonamides).
There are a huge number of drugs 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
According to the mechanism of action, these drugs are divided into six main groups:
- Antibiotics that disrupt the synthesis of cell membrane components: penicillins, cephalosporins, etc.
- Drugs that interfere with the normal functioning of the cell wall: polyenes, polymyxins.
- Drugs that inhibit protein synthesis: macrolides, tetracyclines, aminoglycosides, etc.
- Inhibiting RNA synthesis at the stage of actionRNA polymerases: rifampicins, sulfonamides.
- Inhibiting RNA synthesis at the stage of DNA polymerase action: actinomycins and others.
- Blockers of DNA synthesis: anthracyclines, nitrofurans, etc.
However, this classification is not very convenient. In clinical practice, the following division of antibacterial drugs is accepted:
- Penicillins.
- Cephalosporins.
- Macrolides.
- Aminoglycosides.
- Polymyxins and polyenes.
- Tetracyclines.
- Sulfanilamides.
- Aminoquinolone derivatives.
- Nitrofurans.
- 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. Beta-lactam antibiotics include penicillins, cephalosporins, carbapenems, monobactams. All of them are characterized by high efficiency and relatively low toxicity, which makes them the most commonly prescribed drugs for the treatment of many diseases.
The mechanism of action of beta-lactam antibiotics is due to their structure. Excessive details are useless here, it is worth mentioning 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 is manifested by blocking the synthesis of elements of the pathogen cell wall. However, many bacteria are able to produce a special enzyme that disrupts 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-lactamase in the treatment is ineffective.
Today, antibiotics of the beta-lactam group, protected from the action of a bacterial enzyme, are becoming more widespread. They include substances that block the synthesis of beta-lactamase, for example, clavulonic acid. This is how protected beta-lactam antibiotics (such as Amoxiclav) are created. Other bacterial enzyme inhibitors include Sulbactam and Tazobactam.
Drugs from the penicillin group: historical background
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, it soon became clear that their effectiveness was gradually declining, 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 strains of microbes insensitive to them, therefore, in their pure form, preparations of this group are now ineffective and almost never used. They are best used in combination with substances that increase their bactericidal effect, as well as suppress the defense mechanisms of bacteria.
Penicillin drugs
These are beta-lactam antibiotics, the classification of which is quite extensive:
- Natural penicillins (like "Benzylpenicillin").
- Antistaphylococcal ("Oxacillin").
- Extended-spectrum penicillins ("Ampicillin", "Amoxicillin").
- Antipseudomonal ("Azlocillin").
- Protected penicillins (combined with clavulonic acid, Sulbactam, Tazobactam).
- Preparations containing several penicillin antibiotics.
Summary of drugs belonging to the penicillin group
Natural penicillins are able to successfully suppress the activity of both gram-positive and gram-negative microorganisms. Of the latter, streptococci and the causative agent of meningitis are most sensitive to this group of beta-lactam antibiotics. The rest of the bacteria have now acquired defense mechanisms. Natural penicillins are also effective against anaerobes: clostridia, peptococci, peptostreptococci, etc. These drugs are the least toxic and have a relatively small number of undesirable effects, the list of which is reduced mainly to allergic manifestations, although in case of an overdose, the development of a 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, like Oxacillin. This is a drug for narrow use, sinceIt is intended primarily for the fight against Staphylococcus aureus. It is against this pathogen (including penicillin-resistant strains) that Oxacillin is most effective. Side effects are similar to those of other representatives of this group of drugs.
Extended-spectrum penicillins, in addition to gram-positive, gram-negative flora and anaerobes, are also active against pathogens of intestinal infections. Side effects are the same as above, although these drugs are slightly more likely to cause digestive upset.
Beta-lactam antibiotic "Azlocillin" (representative of the fourth group of penicillins) is designed to combat Pseudomonas aeruginosa. However, at present, this pathogen has shown resistance to 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 contain substances that inhibit bacterial beta-lactamase, they are more effective in the treatment of many diseases.
The last group is a combination of several representatives of the penicillin series, mutually reinforcing each other's action.
Four generations of bacterial exterminators
Beta-lactam antibiotics are also cephalosporins. These drugs, like penicillins, differ in the breadth of the spectrum of action and the insignificance of side effects.
There are four groups (generations) of cephalosporins:
- The brightest representatives of the first generation are Cefazolin and Cefalexin. They are intended primarily for the control of staphylococci, streptococci, meningococci and gonococci, as well as some gram-negative microorganisms.
- The second generation is the beta-lactam antibiotic Cefuroxime. Its area of responsibility includes mainly gram-negative microflora.
- "Cefotaxime", "Ceftazidime" are representatives of the third group of this classification. They are very effective against enterobacteria, and are also capable of destroying nosocomial flora (hospital strains of microorganisms).
- The main drug of the fourth generation is Cefepime. It has all the advantages of the above drugs, in addition, it is extremely resistant to the action of beta-lactamase bacteria and has activity against Pseudomonas aeruginosa.
Cephalosporins and beta-lactam antibiotics are generally characterized by a pronounced bactericidal effect.
Among the adverse reactions to the administration of these drugs, various allergic reactions deserve the most attention (from minor rashes to life-threatening conditions, such as anaphylactic shock), in some cases, digestive disorders are possible.
Reserve facility
"Imipenem" is a beta-lactam antibiotic related togroup of carbapenems. He, as well as the no less famous "Meropenem", in terms of the effectiveness of the impact on the microflora resistant to other drugs, can give odds even 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 cannot be treated with other drugs.
Backup number two
"Aztreonam" is the most prominent 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, Aztreonam is practically insensitive to beta-lactamases, which makes it the drug of choice for severe forms of diseases caused by these pathogens, especially when treatment with other antibiotics is ineffective.
Spectrum of action 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 there is 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… There is a highly effective drug for all these representatives of the pathogenic flora. Of course, there are highly specialized drugs among these antibiotics, but most are still ready to fight several pathogens of infectious diseases at once. Beta-lactam antibiotics are able to resist even representatives of the nosocomial flora, which is the most resistant to treatment.
What are hospital strains?
We are talking about microorganisms that exist in medical institutions. The sources of their appearance are patients and medical staff. Latent, sluggish forms of diseases are especially dangerous. The hospital is an ideal place where carriers of all possible types of infectious diseases gather. And violations of sanitary rules and regulations are fertile ground for this flora to find a niche for existence, where it could live, multiply and acquire resistance to drugs.
The high resistance of hospital strains is primarily due to the fact that, having chosen a hospital institution as their habitat, bacteria get the opportunity to come into contact with various drugs. Naturally, the effect of drugs on microorganisms occurs randomly, without the purpose of destroying them, and in small doses, and this contributes to the fact that representatives of the hospital microflora can develop protection against destructive mechanisms for them, learn to resist them. This is how strains appear, which are very difficult to fight, and sometimes it seems impossible.
Beta-lactam antibiotics in one way or another try to solve this difficult problem. Among them are representativescapable of quite successfully fighting even the most drug-insensitive bacteria. These are reserve drugs. Their use is limited, and they are assigned only when it is really necessary. If these antibiotics are used unreasonably often, then most likely this will end in a drop in their effectiveness, because then the bacteria will have the opportunity 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 primarily due to their spectrum of action. It is best to prescribe a beta-lactam antibiotic for an infection that 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 drugs that can fight Pseudomonas aeruginosa.
Cephalosporins have a similar spectrum of action, so 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 difficult to treat diseases, including those caused by hospital strains. They arealso effective in sepsis and septic shock.
Unwanted action
As already mentioned, beta-lactam antibiotics (drugs belonging to this group are listed above) have a relatively small number of harmful effects on the body. Rarely occurring convulsive syndrome and symptoms of a disorder of the digestive system do not pose a threat to life. Severe allergic reactions to beta-lactam antibiotics can become really dangerous.
Rashes, pruritus, rhinitis and conjunctivitis do not pose a threat to life, although they are very unpleasant. What really should be feared is such severe reactions as Quincke's edema (especially in the larynx, which is accompanied by severe suffocation up to the inability to breathe) and anaphylactic shock. Therefore, the drug can only be administered after an allergy test has been performed.
Cross-reactions are also possible. 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 if one of them is intolerant, all the others will also be perceived by the body as an allergen.
A few words about factors that increase bacterial resistance
The gradual decrease in the effectiveness of antibacterial drugs (including beta-lactam antibiotics) is due to their unreasonably frequent and often incorrect prescription. An incomplete course of treatment, the use of small therapeutic doses do not contribute to recovery, butgive microorganisms the opportunity to “train”, invent and develop methods of protection against drugs. So is it any wonder that the latter become ineffective over time?
Although now antibiotics are not dispensed in pharmacies without a prescription, you can still get them. And this means that self-medication and the problems associated with it (the use of the same drug all the time, unreasonable interruption of the course of therapy, incorrectly selected doses, etc.) will remain, creating conditions for the cultivation of resistant strains.
The hospital flora will not go anywhere either, having the opportunity to actively contact various drugs and invent new ways to counteract them.
What to do? Do not self-medicate, follow the recommendations of the attending physician: take medicines for as long as necessary, and in the correct doses. Of course, it is more difficult to fight the nosocomial flora, but it is still possible. The tightening of sanitary standards and their strict implementation will reduce the likelihood of creating favorable conditions for the reproduction of resistant flora.
A few words in conclusion
Very broad topic - beta-lactam antibiotics. Pharmacology (the science of drugs and their effect on the body) devotes several chapters to them, which include not only a general description of the group, but also contain a description of its most famous representatives. This article does not claim to be complete, it only tries to introduce the mainmoments you need to know about these drugs.
Be he althy and do not forget: before using this or that antibiotic, carefully read the instructions and strictly follow the recommendations, and even better, consult a specialist.
