Classification by chemical structure
This is the basic structural classification that must be known to understand drug affiliation to related groups. The following key classes are distinguished:
- Beta-lactam antibiotics. This is the most extensive and frequently used group. It includes penicillins, cephalosporins, carbapenems, and monobactams.
- Macrolides and azalides.
- Aminoglycosides.
- Tetracyclines.
- Polymyxins.
- Polyene antibiotics (a specific group with pronounced antifungal activity).
- Chloramphenicol preparations (which include levomycetin).
- Glycopeptides.
- Antibiotics of various chemical groups not included in the main categories.
Detailed classification of macrolides
The macrolide group has its own internal classification based on the number of atoms in the lactone ring, as well as the origin of the drug (natural or semi-synthetic):
- 14-membered macrolides:
- Natural: Erythromycin, Oleandomycin.
- Semi-synthetic: Roxithromycin, Clarithromycin.
- 15-membered macrolides (Azalides):
- Represented by semi-synthetic drugs, the main one being Azithromycin.
- 16-membered macrolides:
- Natural: Spiramycin, Josamycin, Midecamycin.
- Semi-synthetic: Midecamycin.
Division by spectrum of antimicrobial action
Antibiotics are divided into three large groups depending on their ability to affect gram-positive (G+) and gram-negative (G-) flora:
- Broad-spectrum drugs. They act effectively on both G+ and G- bacteria. This category includes tetracyclines, chloramphenicol (levomycetin), aminoglycosides, cephalosporins, and semi-synthetic penicillins.
- Drugs with predominant action on gram-positive (G+) bacteria. This group includes macrolides and biosynthetic (natural) penicillins.
- Drugs with predominant action on gram-negative (G-) bacteria. This includes polymyxins and monobactams.
Classification by the nature of action on the cell
This division is based on the specific effect the drug exerts on the bacterial cell during treatment:
- Bactericidal antibiotics. Cause irreversible death (lysis) of bacterial cells. The pathogen is completely destroyed.
- Bacteriostatic antibiotics. Stop the growth and division of bacteria (inhibit their reproduction), but do not kill microorganisms directly.
Important rule of pharmacotherapy: when prescribing treatment, it is necessary to strictly consider the nature of the drug's action. Special attention is paid to joint administration: the combination of bacteriostatic and bactericidal agents requires extreme caution.
Classification by clinical use and sources
Depending on origin (sources of derivation), antibiotics are divided into natural (biosynthetic), which are products of the vital activity of microorganisms and lower fungi, and semi-synthetic, created artificially through chemical modification of natural molecules.
Depending on the prescription tactics in clinical practice, two categories are distinguished:
- Primary antibiotics (drugs of choice). These are first-line agents. They are prescribed first for empirical therapy. The use of these drugs begins immediately, even before receiving the results of the antibiogram (laboratory determination of pathogen susceptibility).
- Reserve antibiotics. Used strictly as a "second line". Indications for their prescription are identified resistance of microorganisms to primary drugs or individual intolerance to primary drugs by the patient.
Briefly: answers to topical questions
Which representatives are included in the aminoglycoside group?
The aminoglycoside group includes natural (produced by fungi of the genera Actinomyces and Micromonospora) and semi-synthetic drugs, which are classified into three generations.
- Streptomycin, neomycin, kanamycin are 1st generation drugs.
- Gentamicin, tobramycin, netilmicin are 2nd generation drugs.
- Amikacin is a 3rd generation drug.
These antibiotics are similar in properties, but differ in the spectrum of activity and bacterial resistance profile.
What side effects are characteristic of aminoglycosides?
Aminoglycoside drugs are characterized by high toxicity with the development of a number of serious adverse reactions.
- Ototoxicity — hearing loss and damage to the vestibular apparatus.
- Nephrotoxicity — kidney damage.
- Hepatotoxicity — liver function impairment.
- Dyspeptic disorders — nausea, vomiting, diarrhea.
The severity of side effects may vary among different representatives; for example, netilmicin has a less pronounced ototoxic effect.
What drugs are included in the tetracycline group?
The tetracycline group includes natural and semi-synthetic drugs, which are divided by duration of action.
- Tetracycline — a short-acting natural biosynthetic antibiotic (6–8 hours).
- Oxytetracycline — a short-acting natural biosynthetic antibiotic.
- Methacycline (Rondomycin) — a long-acting semi-synthetic drug (12–24 hours).
- Doxycycline (Vibramycin) — a long-acting semi-synthetic drug.
The chemical structure of these drugs is based on four condensed six-membered rings.
To remember the broad-spectrum antibiotic groups, use the mnemonic: "Whole Army Takes Good Care". The first letters correspond to the groups: Cephalosporins, Aminoglycosides, Tetracyclines, Chloramphenicol, Semisynthetic penicillins.
Class and exam questions
What is the difference in the spectrum of action between natural and semisynthetic penicillins?
Natural (biosynthetic) penicillins have a predominant effect on Gram-positive (G+) bacteria. Semisynthetic penicillins belong to broad-spectrum drugs and act effectively on both Gram-positive and Gram-negative flora.
Can bactericidal and bacteriostatic antibiotics be prescribed together?
This must be done with great caution. According to clinical principles, the co-administration of drugs, one of which causes bacterial lysis while the other merely inhibits their growth, requires careful monitoring.
What are reserve antibiotics and in what cases are they used?
These are drugs used as a "second line". They are prescribed only when microorganisms develop resistance (resistence) to the primary drugs of choice, or if the patient is intolerant to the main medications.
What else to study on this topic
- Structural features of the beta-lactam ring and mechanisms of its degradation.
- Principles of antibiogram testing and result interpretation.
- Mechanisms of bacterial resistance development to major drugs.
- Pharmacokinetic differences between 14-membered and 15-membered macrolides.
- Specifics of using polyene antibiotics in fungal infections.
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