Cephalosporins: The foundation of β-lactam therapy
Cephalosporins represent a crucial group of β-lactam antibiotics with the broadest possible spectrum of antimicrobial activity. They are characterized by a bactericidal type of action, meaning they completely destroy bacterial cells.
In their chemical structure, cephalosporins are very close to penicillins. The basis of their molecule is 7-aminocephalosporanic acid. It contains a specific β-lactam ring, which determines the mechanism of antimicrobial action. The main clinical advantage of cephalosporins over penicillins lies in their high resistance to the action of β-lactamases—enzymes produced by microorganisms to neutralize drugs.
Macrolides, azalides, and fusidins
Macrolides and azalides have a specific spectrum of activity. They are effective against microorganisms such as Clostridium spp., Corynebacterium diphtheriae, Haemophilus influenzae, Mycoplasma pneumoniae, Actinomyces israelii, Listeria monocytogenes and Chlamydia. An important feature of their pharmacokinetics is that, upon systemic administration, they penetrate the blood-ophthalmic barrier (BOB) poorly. Therefore, topical application is often warranted. Popular agents include Erythromycin ointment (containing 10,000 IU/g of erythromycin) and Azyter drops (0.15% azithromycin solution, prescribed to children from 1 year of age, twice daily).
Fusidins exert a bacteriostatic effect and act primarily against staphylococcal flora. These are reserve antistaphylococcal drugs used in case of allergy to β-lactams or proven resistance to them. Like macrolides, fusidins cross the BOB poorly. Fucithalmic (1% fusidic acid) is used as a topical agent.
Combination drugs: Component synergy
Combinations of antibiotics are used to combat complex infections. Currently, the unique drug containing three antibacterial components simultaneously is Colbiocin.
- Chloramphenicol. A broad-spectrum antibiotic that inhibits protein synthesis in susceptible microbes. It destroys gram-positive and gram-negative bacteria, as well as Mycoplasma spp., Rickettsia spp., and Chlamydia spp. It is inactive against Pseudomonas aeruginosa and fungi.
- Rolitetracycline (tetracycline group). It has a bacteriostatic effect, blocking bacterial protein synthesis at the RNA level. The spectrum includes gram-negative bacteria, chlamydiae, mycoplasmas, rickettsiae, and protozoa (Entamoeba histolytica). Microbial resistance to it develops slowly.
- Colistin (polymyxin E). A bactericidal antibiotic isolated from Bacillus polymyxa var. colistinus. It is active against most gram-negative bacteria (including Pseudomonas spp. and Haemophilus spp.) and fungi. This is a "deep" reserve drug for treating multidrug-resistant infections. Colistin shows no cross-resistance with broad-spectrum antibiotics and exhibits pronounced synergy with them.
Prevention of complications: Polyene antibiotics
Massive broad-spectrum antibiotic therapy frequently leads to microflora imbalance. To prevent and treat candidiasis (fungal infections of the skin, mucous membranes of the mouth, pharynx, vagina, and intestines), polyene antibiotics are used.
Their key pharmacokinetic feature is that upon oral administration, they are practically unabsorbed from the gastrointestinal tract. Due to this, polyenes exert an exclusively local effect within the intestinal lumen. Among the side effects of polyenes, allergic reactions and various dyspeptic disorders are most common.
To memorize the composition of the combination drug Colbiocin, use the mnemonic CTR: Chloramphenicol, Tetracycline (rolitetracycline), Reserve colistin.
Class and exam questions
Why are cephalosporins often more effective than penicillins?
Unlike penicillins, cephalosporins possess greater structural resistance to β-lactamases—enzymes that bacteria use to destroy antibiotics.
In what cases is colistin prescribed?
Colistin is a "deep-reserve" drug. It is used exclusively for infections caused by gram-negative microorganisms with multidrug resistance to other classes of drugs.
Why are polyenes prescribed during broad-spectrum antibiotic treatment?
Polyene antibiotics are used to prevent candidiasis. They prevent the overgrowth of fungal flora that often occurs against the background of the suppression of normal bacteria by antibiotics.
What else to study on this topic
- The mechanism of action of the β-lactam ring on the bacterial cell wall.
- Classification of cephalosporins and their spectrum of activity.
- Pharmacokinetics of macrolides upon systemic administration.
- Mechanisms of bacterial resistance development to chloramphenicol.
- Features of the use of reserve antistaphylococcal drugs.
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