Pharmacology—Introduction to Antimicrobial Agents

This is a mind map about pharmacology - an introduction to antibacterial drugs, including the mechanism of action of antibacterial drugs, the resistance mechanism of antibacterial drugs, and the principles of rational application of antibacterial drugs.

Edited at 2023-11-23 09:34:56

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Pharmacology—Introduction to Antimicrobial Agents

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039 Introduction to Antibacterial Drugs

Chemotherapy (chemotherapy) – drug treatment primarily targeting diseases caused by all pathogens, including microorganisms, parasites, and even tumor cells

antiparasitic drugs

anti-malignant tumor drugs

antimicrobial drugs

antibacterial drugs

antifungal drugs

antiviral drugs

Common terms for antibacterial drugs

Antibacterial drugs: drugs that inhibit or kill bacteria, including antibiotics and synthetic drugs (made by chemical methods) Antibiotics: Substances produced by various microorganisms (bacteria, fungi, actinomycetes, etc.) that can kill or inhibit other microorganisms. Divided into natural antibiotics (produced by microorganisms) and artificial semi-synthetic antibiotics (obtained by structural modification of natural antibiotics) Antibacterial spectrum: The antibacterial range of antibacterial drugs, including broad spectrum (effective against a variety of pathogenic microorganisms - tetracycline, chloramphenicol, third and fourth generation fluoroquinolones) and narrow spectrum (effective against only one type of bacteria or limited to a certain genus of bacteria) Effective - Isoniazid is only effective against Mycobacterium tuberculosis)

Antibacterial activity: the ability of antibacterial drugs to inhibit or kill pathogenic microorganisms

Bacteriostatic drugs: Antibacterial drugs that only inhibit the growth and reproduction of bacteria without killing them (tetracyclines, erythromycins, sulfonamides) Bactericidal drugs: antibacterial drugs that kill bacteria (penicillins, cephalosporins, aminoglycosides)

Minimum inhibitory concentration MIC: The lowest drug concentration that can inhibit the growth of pathogenic bacteria in the culture medium after culturing bacteria in vitro for 18-24 hours. Minimum bactericidal concentration MBC: the lowest drug concentration that can kill bacteria in the culture medium or reduce bacteria by 99.9%

Chemotherapy index CI: an index to evaluate the effectiveness and safety of chemotherapy drugs, based on the ratio of the half lethal dose LD₅₀ of the chemotherapy drug to the half effective dose ED₅₅ for treating infected animals (LD₅₀/ED₅₀) or LD₅/ED₉₅. The larger the safer it is, clinically The higher the application value, but it is not absolute. For example, penicillin has a large chemotherapy index and is almost non-toxic to the body, but anaphylactic shock may occur. Post-antibiotic effect (PAE): Bacteria are in brief contact with antibiotics. After the concentration of the antibiotic drops, falls below the MIC or disappears, the bacterial growth is still inhibited. Features: When PAE exists, antibacterial drugs are concentration-dependent; the same antibacterial drug has different PAEs against different bacteria. First contact effect: Antibacterial drugs have a strong antibacterial effect when they come into contact with bacteria for the first time. This strong effect no longer appears when they are exposed again, or the antibacterial effect is no longer significantly enhanced after continuous contact with bacteria, and it takes a considerable period of time to take effect (amino- glycosides)

Mechanism of action of antibacterial drugs

Mainly by specifically interfering with the biochemical metabolic process of bacteria, affecting their structure and function, causing them to lose their ability to reproduce normally, thereby inhibiting or killing bacteria.

① Inhibit bacterial cell wall synthesis: has no effect on the synthesized cell wall, mainly inhibits peptidoglycan, bacterial reproduction period ②Change the permeability of the cytoplasmic membrane: Impair the permeability of the cell membrane, leakage of bacterial substances, resulting in bacterial death, bacterial quiescence ③Inhibit protein synthesis: Ribosomes are the site of protein synthesis ④Influence nucleic acid and folic acid metabolism

Antimicrobial resistance mechanisms

Drug resistance - the reduced sensitivity of pathogens or tumor cells to repeated applications of chemotherapeutic drugs

Resistant species

Intrinsic resistance (natural resistance): determined by bacterial chromosomal genes, passed from generation to generation, and will not change (streptococci are naturally resistant to aminoglycoside antibiotics, intestinal gram-negative bacteria are naturally resistant to penicillin G, aeruginosa Pseudomonas is not susceptible to most antibiotics)

Acquired resistance: After contact with antibiotics, it changes its metabolic pathway to prevent it from being killed by antibiotics (Staphylococcus aureus produces β-lactamase and is resistant to β-lactamase antibiotics)

mechanism

produce inactivating enzyme

Changes in target sites of antibacterial drugs

Change bacterial outer membrane permeability

Affect active outflow system

Principles of rational application of antibacterial drugs

Identify pathogenic bacteria as early as possible

①Cultivation of pathogenic bacteria and in vitro antimicrobial susceptibility testing, so as to select antimicrobial drugs in a targeted manner ② If the patient’s infection symptoms are severe, the most likely pathogenic bacteria can be predicted based on clinical diagnosis ③According to changes in bacterial sensitivity and resistance to various antibacterial drugs, select appropriate drugs for empirical treatment ④ For unexplained fever or viral infection, avoid the abuse of antibiotics

Select drugs according to indications

①Select drugs based on their distribution characteristics in the body ② When it is difficult to reach the therapeutic concentration at the infected site after systemic administration, topical medication can be added as auxiliary treatment. ③Avoid using varieties that are mainly intended for systemic application for local use.

Preventive use of antibacterial drugs

① Benzathine penicillin, procaine penicillin or erythromycin are commonly used in children with rheumatic heart disease and children and adults who often suffer from streptococcal pharyngitis or rheumatic fever to prevent the onset of rheumatic fever, and the prevention requires more than several years of treatment. Take medication until your condition is stable ②If it is the season when meningococcal meningitis occurs, oral sulfadiazine can be used as a preventive medication. ③People entering malaria areas should start taking the compound preparation of pyrimethamine and sulfadoxine two weeks before entering, and the time should not exceed 3 months. ④ Penicillin, amoxicillin, and cefazolin can be used respectively for patients with rheumatic heart disease and congenital heart disease with artificial valves before oral, upper respiratory tract, urethral and cardiac surgery. ⑤ Use penicillin or amoxicillin for patients with war wounds, combined trauma, and vasculitis obliterans after amputation to prevent gas gangrene caused by Clostridium perfringens. Those who are allergic to penicillin can use clindamycin or amoxicillin. Nitrodazole ⑥ Take medication for 1 to 3 days after gastrointestinal, thoracic and abdominal surgery

Antibacterial drug combinations

Indications

①Serious infection with unknown pathogen ②Infections that cannot be controlled by a single drug ③Can reduce drug toxicity and adverse reactions ④Infected areas where a single drug cannot easily penetrate ⑤ Long-term chronic infection with severe drug resistance

Classification

(I) Bactericidal drugs during the breeding period such as penicilliums and cephalosporins (II) Stationary phase bactericidal drugs such as aminoglycosides and polymyxins (III) Rapid antibacterial drugs such as tetracyclines and macrolides (IV) Slow-acting bacteriostatic drugs such as sulfonamides Possible effects: I II = synergy I III=antagonistic III IV = Addition I IV = irrelevant/additive

When used in combination, there should be a synergistic or additive effect It is best to use no more than 3 types of antibiotics in combination Avoid co-administration of drugs with the same toxicity Avoid co-administration of drugs with the same mechanism of action Pay attention to the incompatibility between drugs when using them together

Prevent the irrational use of antibacterial drugs

Viral infections and fever of unknown origin generally do not need to be treated with antibiotics Avoid topical application of antibacterial drugs, otherwise it may cause bacterial tolerance and allergic reactions

other factors

① People with reduced liver function: avoid using antibacterial drugs that are mainly metabolized by the liver and cause damage to the liver, such as erythromycin, rifampicin, tetracyclines, chloramphenicol, lincomycin, etc. ② People with reduced renal function: avoid using antibacterial drugs that are mainly excreted by the kidneys and cause damage to the kidneys, such as aminoglycosides, amphotericin B, vancomycin, first-generation cephalosporins, etc. ③ Neonates, children, pregnant women and lactating women should be careful when using medication and be sure to choose safe antibacterial drugs.