Practical 1: Antibiotics

Antibiotics and Antiinfectives

  • Antiinfectives: Substances for the treatment of infectious diseases.

    • I. Antibacterics: Against bacteria.

    • II. Antimycotics: Against moulds and yeasts.

    • III. Antivirotics: Against viruses.

Antibacterics

  • Classification according to Chemical Structure:

    1. Antibiotics: Products of metabolism of microorganisms.

    2. Chemotherapeutics

      • a) Sulfonamides

      • b) Quinolones

      • c) Nitrofurans.

  • Features of Antibiotics:

    • Kill other microorganisms or stop their growth.

    • Most crucial group of medications in animals.

    • Replaced by semi-synthetic and synthetic substances for broader efficacy, availability, and cost.

History of Antibiotics Development

  • 1929: Penicillin (A. Fleming).

  • 1942: Benzylpenicillin.

  • 1944: Streptomycin.

  • 1948: Chlortetracyclin.

  • 1949: Chloramphenikol, Neomycin.

  • 1950: Oxytetracycline.

  • 1952: Erythromycin.

  • Continuing developments up to 2015 with Teixobactin.

Classification According to Chemical Structure (Page 2)

  1. Penicillins: Benzylpenicillin, Amoxicillin, Ampicillin, Beta-lactams.

  2. Cefalosporins: Cefalexin, Ceftiofur.

  3. Tetracyclins: Tetracycline, Oxytetracycline, Chlortetracycline.

  4. Amfenicols: Florfenicol.

  5. Polypeptides and Glycopeptides: Colistin, Polymyxin B.

  6. Aminoglycosides: Gentamicin, Streptomycin, Neomycin.

  7. Macrolides: Erythromycin, Tylosin, Tilmicosin.

  8. Lincosamides: Lincomycin, Clindamycin.

  9. Ansamycins: Rifaximin.

  10. Diterpens: Tiamulin, Valnemulin.

  11. Antibiotics with Different Structures: Novobiocin, Fusidic acid.

Penicillins

  • Types:

    • A. Narrow Spectrum: Benzylpenicillin, Phenoxymethylpenicillin.

    • B. Broad Spectrum: Ampicillin, Amoxicillin.

    • C. Beta-lactamase Resistant: Dicloxacillin, Nafcillin.

Pharmacokinetics of Penicillin Salts

  • MIC: Minimum Inhibitory Concentration (0.03 IU/ml).

Cefalosporins Classification

  1. First Generation: Cefacetrile, Cefalexin.

  2. Second Generation: Cefoxitin, Cefotetan.

  3. Third Generation: Cefoperazone.

  4. Fourth Generation: Cefquinone.

Antibiotics' Mechanism of Action (Page 4)

  1. Cell Envelope Antibiotics: Inhibit cell wall synthesis (β-lactams, Glycopeptides, Polymyxins).

  2. Protein Synthesis Inhibitors: Tetracyclines, Amphenicols, Aminoglycosides, Macrolides, Lincosamides.

  3. Nucleic Acids Synthesis Inhibitors: Rifamicins.

Classification of Antibiotics by Their Effects

  • Bacteriostatic: Suppresses growth (e.g., Tetracyclines).

  • Bactericidal: Kills bacteria (e.g., β-lactam antibiotics).

Spectrum of Action

  1. Broad-Spectrum Antibiotic: Effective against a wide range (both G+ and G- bacteria) - e.g., Tetracyclines.

  2. Slightly Broad-Spectrum Antibiotic: e.g., Ampicillin.

  3. Narrow-Spectrum Antibiotic: Specific families of bacteria - e.g., Penicillin G.

Adverse Effects of Antibiotics (Page 5)

  1. To Animals:

    • Allergic reactions, salivation, emesis, disruption of intestinal flora, diarrhea, reduction of B vitamin synthesis, resistance development.

  2. Animal-Origin Products:

    • Depreciation of meat quality, injection site issues, processing difficulties.

  3. To Humans:

    • Residues in food products, resistance development.

Resistance of Microorganisms

  1. Primary Resistance: Naturally unresponsive bacteria (e.g., Mycobacterium tuberculosis).

  2. Secondary Resistance: Acquired through genetic changes.

Antibiotic Effectiveness Testing Methods (Page 6)

  1. Diffusion: Disc diffusion method (qualitative), E-test (quantitative).

  2. Dilution:

    • Microdilution (96-well plates).

    • Macrodilution (tubes).

Disc Diffusion Method

  • Antibiotics disc placed on bacterial culture; measure inhibition zone.

E-Test

  • Quantitative method using a strip with a concentration gradient.

Dilution Methods

  • Quantitative method for MIC determination:

    • Macrodilution: Liquid medium in tubes.

    • Microdilution: Liquid medium in microplates with varying concentrations of the antibiotic.

Dilution of Antibiotics (Page 7)

  • Many injectable antibiotics are unstable in solutions/suspensions and must be prepared shortly before administration.

  • Common solvent: Water for injection.

  • Preparation Procedure:

    • Clean the stopper, inject water, and prepare suspension gently to avoid foaming.

Required Amounts for Preparation of Solutions

  • Water for injection amounts vary by antibiotic formulation (e.g., Penicillin G).

  • Specific guidelines for water volumes based on antibiotic dosages.