First of all, it is necessary to determine the terms used in medicine. Drugs for the treatment of infectious diseases of humans are one of the most numerous groups of medicines, and their division into groups is based on the classification of pathogens. Currently, there are six groups of infectious agents: prions, viruses, bacteria, fungi, parasitic protozoa, parasitic worms and anthropods (arthropods). Based on this, there are six different groups of anti — infectious chemotherapy drugs, respectively-antiviral, antibacterial, antifungal, anthelmintic, etc., and the most widespread are antibacterial drugs, that is, drugs that affect only bacteria.
Although the term " antibiotic” is often used in relation to all antibacterial agents, true antibiotics are only substances that selectively inhibit the vital activity of bacteria. The selective action should be understood as the activity of the drug only against microorganisms while maintaining the viability of the host cells and the effect is not on all, but only on certain types of microorganisms. This is how antibiotics differ from antiseptics, which act on microorganisms indiscriminately and are used to destroy them in living tissues, and disinfectants intended for the indiscriminate destruction of microorganisms outside a living organism (care items, surfaces, etc.).
Traditionally, antibacterial drugs continue to be divided into natural (antibiotics themselves, for example, penicillin), semi-synthetic (products of modification of natural molecules, for example, aminopenicillins or cephalosporins) and synthetic (for example, sulfonamides, nitrofurans). However, at present, this division has lost its relevance, since a number of natural antibiotics are obtained by synthesis (chloramphenicol), and some drugs called antibiotics (fluoroquinolones) are actually synthetic compounds.
From a practical point of view, it is more important to divide into groups and classes based on their chemical structure, according to which beta-lactam antibiotics (penicillins, cephalosporins, carbapenems), aminoglycosides, macrolides, tetracyclines, etc. are isolated. It is the chemical structure of the antibiotic that determines the mechanism of its action, the spectrum of antibacterial activity, the pharmacokinetic features of the drug (absorption, distribution and excretion from the patient's body), the nature of adverse reactions, the tolerability of the drug, etc.
However, despite the many common features that unite antibacterial drugs, it would be wrong to consider all drugs belonging to the same group as absolutely interchangeable. Each antibiotic has quite specific properties, which are given in detail in special reference books and manuals on antibacterial therapy and which must be taken into account when prescribing them.
For example, among the third generation of cephalosporins, only 2 antibiotics have clinically significant activity against Pseudomonas aeruginosa, a frequent and formidable pathogen of nosocomial infections: ceftazidime and cefaperazone. Therefore, with a high risk of developing this infection, the appointment of other antibacterial drugs from the same group would be a mistake, since the results of clinical trials indicate a high frequency of failures of such treatment. Another example is the difference in the pharmacokinetics of antibacterial drugs: ampicillin and amoxicillin, which belong to the group of aminopenicillins and have almost the same spectrum of antimicrobial activity, have completely different bioavailability (ampicillin is poorly absorbed from the gastrointestinal tract), which causes the use of different regimens of these drugs.