Microbiological principle
The basis of effective treatment is the accurate identification of the pathogen and the determination of its drug susceptibility.
- Ideal scenario (targeted approach): The physician precisely knows the microbial species and has its antibiogram available. In this case, a narrow-spectrum drug is prescribed, hitting the exact target — the specific pathogen.
- Empirical approach: If the pathogen is unknown, treatment begins with broad-spectrum drugs to reliably cover the most likely culprits of the infection.
In 2–3 days, when the bacteriological culture results arrive, de-escalation is performed — the regimen is adjusted and switched to targeted therapy. It is important to start treatment as early as possible: at the onset of the disease, the microbial load is low, and drugs are much more effective at destroying actively dividing cells.
Pharmacological principle
This principle requires taking into account the pharmacokinetics and pharmacodynamics of the drug. The main task is to successfully deliver the active substance directly to the site of inflammation.
- Regimen and doses: It is necessary to create a concentration of the substance in tissues that ensures a reliable microbistatic (growth arrest) or microbicidal (destruction) effect. The dose is selected taking into account distribution in the body and administration frequency.
- Duration: The course must last exactly as long as needed for the complete eradication of the microbe. Relying solely on the disappearance of symptoms is unacceptable.
- Routes of administration: The physician must account for the body's barriers. For example, in certain infections, oral administration is ineffective due to poor absorption, whereas in meningitis, it is crucial to choose drugs capable of penetrating the blood-brain barrier.
Clinical principle
The choice of antibiotic is inextricably linked with the individual characteristics of the patient. Treatment must be not only effective, but also safe.
When prescribing, age, sex, presence of pregnancy, and immune status are evaluated. It is critically important to consider comorbid conditions and the function of excretory organs (liver and kidneys) to avoid systemic toxicity.
Tactic in severe infections: If the patient's condition is life-threatening, timeliness and maximum breadth of coverage come to the fore. In such situations, combinations of 2–3 drugs are used. At the same time, strict combination rules apply:
- Efficacy: Drugs must work synergistically, without mutual suppression of antibacterial activity (antagonism).
- Safety: The combination of drugs whose toxic effects can be additive is strictly prohibited.
Epidemiological and pharmaceutical approaches
For successful therapy, it is important to assess the global and local context.
- Epidemiology: The physician must know the current local resistance pattern — which strains are circulating in a specific region, hospital, or even an individual ward. It is important to remember that antibiotic resistance is a reversible process. Bacteria can lose acquired resistance, returning to their natural susceptibility.
- Pharmaceutics: Special attention is paid to the storage conditions and expiration dates of antibacterial agents. Violation of these rules leads not just to a loss of therapeutic effect. Due to chemical degradation of the active substance, the drug may become toxic. Also, when choosing a treatment regimen, one should not forget about the economic aspect and the cost of the course for the patient or clinic.
Briefly: answers to topical questions
What are the indications for prescribing combination antibiotic therapy?
Combination antibiotic therapy is used in severe infections to provide the widest possible spectrum of activity. The main indications for its prescription are septic course, microbial associations, atypical flora, and the need to overcome high multi-resistance. In addition, combinations of several drugs are used in life-threatening conditions to achieve a reliable clinical effect.
Which antibiotic groups have a bactericidal type of action?
The following groups of antimicrobial agents have a bactericidal type of action:
- beta-lactam antibiotics (beta-lactama) — include penicillins, cephalosporins, carbapenems, and monobactams;
- glycopeptides (glycopeptida) — disrupt the synthesis of the bacterial cell wall;
- aminoglycosides (aminoglycosida) — drugs that disrupt intracellular protein synthesis;
- rifamycins (rifamycina) — antibiotics that disrupt RNA synthesis.
Which antibiotics are capable of penetrating the blood-brain barrier in meningitis?
Antibiotics with high permeability across the blood-brain barrier are used to treat central nervous system infections and meningitis. These include:
- cephalosporins — ceftriaxone, cefotaxime, and ceftazidime;
- carbapenems — meropenem;
- aminoglycosides — gentamicin;
- penicillins — amoxicillin;
- glycopeptides — vancomycin.
What are the main mechanisms of acquired antibiotic resistance in bacteria?
The main mechanisms of acquired antibiotic resistance in bacteria include the following adaptive changes:
- substrate overproduction (hyperproductio) — excessive synthesis of substances in response to enzyme blockade;
- target mutation (mutatio) — structural modification of enzymes at binding sites, reducing affinity for the drug;
- decreased permeability (permeabilitas) — reduction of cell membrane permeability to drug substances;
- active efflux (efflux) — pumping the drug out of the cell using special transport pumps.
What routes of antibiotic administration are used in clinical practice?
Various routes of antibiotic administration are used in clinical practice depending on the severity of the patient's condition and the pharmacokinetic properties of the agents:
- oral route (per os) — administration by mouth for outpatients and when absorption is good;
- parenteral route (parenteraliter) — intravenous or intramuscular administration, used for severe infections and hospitalization;
- intraosseous and regional routes (intraossalis et regionalis) — used in surgical infections;
- intraperitoneal route (intraperitonealis) — used in the treatment of peritonitis via special drains.
To memorize the basic principles, use the "MFK" rule: Microbiological, Pharmacological, Clinical, Epidemiological.
Class and exam questions
Why shouldn't you stop taking antibiotics as soon as you feel better?
Clinical improvement does not mean that the pathogen has been completely eradicated. Premature discontinuation will leave surviving microbes in the body, leading to a relapse of the disease.
What is the difference between empiric and targeted therapy?
Empirical therapy uses broad-spectrum drugs and is prescribed before the exact pathogen is identified. Targeted therapy is used when the microbe is known and acts narrowly based on antibiogram data.
What are the main rules for combining antibiotics in severe infections?
The combination must have a synergistic effect. At the same time, the drugs must not reduce each other's antibacterial activity (antagonism) or have additive toxic effects.
What else to study on this topic
- Concept and calculation of the minimum inhibitory concentration (MIC)
- Algorithm for performing de-escalation antibiotic therapy
- Permeability of histohematic barriers to antibiotics
- Mechanisms of development and loss of antibiotic resistance
- Toxic effects of antibacterial drug degradation
Study the full topic in the «Microbiology» course
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