Antimicrobial Agents

Antimicrobial Agents

Overview of Antibacterial Agents

  • Divisions of Antibacterial Agents:
    • Bactericidal: Kill bacteria.
    • Bacteriostatic: Inhibit the reproduction and growth of bacteria.
    • Elimination Process: The removal of bacteria depends on the phagocytosis by leukocytes and macrophages.

Sources of Antibacterial Drugs

  • Methods of Obtaining Antibacterial Drugs:
    1. From microorganisms.
    2. Through chemical synthesis.

Antibacterial Substances from Microorganisms

  • Production by Microorganisms:
    • Microorganisms produce substances that inhibit the growth of other bacteria.
    • Example: Penicillin, derived from the fungus Penicillium notatum, inhibits the growth of Gram-positive bacteria.
    • Only a few antibacterial drugs are effective against both Gram-positive and Gram-negative bacteria.
    • Antibacterial drugs that are effective against both types are known as broad-spectrum antibiotics.

Classification of Penicillins

  • General Characteristics of Penicillins:
    • Classified as bactericidal.
    • Act by intervening in the synthesis of the bacterial cell wall.
    • Generations of Penicillins:
    • First Generation
    • Second Generation
    • Third Generation
    • Fourth Generation
First Generation Penicillins
  • Effectiveness: Against Gram-positive bacteria (e.g., streptococci and diplococci).
  • Examples: Penicillin G and Penicillin V.
  • Adverse Effects: Allergies.
Second Generation Penicillins
  • Effectiveness: Against both Gram-positive and Gram-negative bacteria including E. coli, Proteus mirabilis, and Haemophilus influenzae.
  • Examples: Ampicillin and Amoxicillin (broad spectrum).
  • Combination: Amoxicillin combined with clavulanic acid results in Augmentin (broad spectrum).
Third Generation Penicillins
  • Spectrum: Broader than second generation.
  • Uses: For infections caused by Pseudomonas and Proteus vulgaris.
  • Example: Geocillin.
Fourth Generation Penicillins
  • Potency: More powerful than earlier generations.
  • Uses: For infections caused by Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumoniae, and Bacteroides fragilis.
  • Examples: Azlin and Mezlocillin sodium.

Cefalosporins

  • Characteristics: Bactericidal and have a structure similar to penicillins; interfere with bacterial cell wall synthesis.
  • Broad Spectrum: Effective for various infections; particularly useful for patients allergic to penicillin.
First Generation Cefalosporins
  • Effectiveness: Against both Gram-positive and Gram-negative bacteria, such as Klebsiella pneumoniae.
  • Examples: Cefadroxil (Duricef) and Cephalexin (Keflex).
Second Generation Cefalosporins
  • Power: More potent than first generation.
  • Effectiveness: Against Gram-negative infections.
  • Examples: Cefaclor (Ceclor) and Cefoxitin (Mefoxin).
Third Generation Cefalosporins
  • Power: More potent with longer effects than prior generations.
  • Uses: Target severe Gram-negative infections.
  • Examples: Cefoperazone (Cefobid) and Cefotaxime (Claforan).

Aminoglycosides

  • Characteristics: Broad-spectrum bactericides that inhibit bacterial protein synthesis.
  • Effectiveness: Particularly effective against Gram-negative bacilli.
  • Examples: Gentamicin (Garamycin) and Neomycin (Neobiotic).

Tetracyclines

  • Characteristics: Broad-spectrum antibiotics effective against both Gram-positive and Gram-negative bacteria.
  • Mechanism: Interfere with bacterial protein synthesis (bacteriostatic).
  • Examples: Tetracycline (Achromycin) and Doxycycline (Vibramycin).
  • Contraindications: Not recommended for pregnant women and children under 7 years old as they may affect tooth development.

Sulfonamides

  • Effectiveness: Active against both Gram-positive and Gram-negative bacteria.
  • Resistance: Significant bacterial resistance has developed due to extensive use.
  • Current Usage: Primarily for treating urinary infections.
  • Examples: Septra, Bactrim, and Silver sulfadiazine (Silvadene).

Other Medications

  • Isoniazid (INH): Used for tuberculosis treatment.
  • Erythromycin (Erythrocin): A macrolide that inhibits protein synthesis; treatment for Mycoplasma pneumoniae and Chlamydial infections.
  • Chloramphenicol: A broad-spectrum antibiotic reserved for serious infections like typhoid fever; inhibits bacterial protein synthesis (bacteriostatic).

Mechanisms of Action of Antibiotics

  • Cell Wall Synthesis Inhibitors:
    • Beta-lactams (e.g., penicillins, cephalosporins).
    • Examples include Vancomycin and Bacitracin.
  • Cell Membrane Disruptors:
    • Polymyxins.
  • Nucleic Acid Synthesis Inhibitors:
    • Interfere with DNA gyrase and RNA polymerase.
    • Quinolones and Rifampicin.
  • Protein Synthesis Inhibitors:
    • Act on 50S ribosomal subunit (e.g., Macrolides, Clindamycin, Linezolid) and 30S ribosomal subunit (e.g., Tetracyclines, Aminoglycosides, Streptogramins).

Antifungal Agents

  • Usage: For treating diseases caused by fungi (mycosis).
    • Examples:
    • Amphotericin B (Fungizone): Used for systemic infections and candidiasis.
    • Clotrimazole (Lotrimin): Treatment for Candida albicans infections.
    • Miconazole (Micatin, Monistat): Treats dermatophytic and candidiasis infections.
    • Nystatin: Used for Candida albicans infections.
Pathogenic Fungi and Systemic Drugs
  • Pathogenic Fungi: Sorted by type and place of infection.
    • Examples:
    • Systemic | Blood, lungs, bones | Histoplasmosis | Amphotericin B
    • Dermatophytes | Skin, hair, nails | Athlete's foot | Griseofulvin
    • Opportunistic (Candida) | Skin, mucous membranes | Vaginal yeast infection | Amphotericin B, Miconazole, Nystatin
Available Antifungal Drugs: Categories
  • By Application:
    • Parenteral: Amphotericin B.
    • Systemic Oral: Griseofulvin, azoles, terbinafine.
    • Topical: Azoles, Nystatin.

Antiviral Drugs

  • Usage: Combat infections caused by viruses by inhibiting viral replication.
    • Examples:
    • Acyclovir (Zovirax): Used for herpes simplex treatment.
    • Amantadine and Tamiflu: Reduce severity of influenza.
Classification of Antiviral Drugs
  1. Antiherpesviruses: Nucleoside analogs.
  2. Anti-influenza: Neuraminidase inhibitors, such as amantadine.
  3. Antiretrovirals: Reverse transcriptase inhibitors, protease inhibitors.
  4. Others: Interferons, ribavirin, and fusion inhibitors.

Antihelmintic Drugs

  • Target: Parasitic worms that infect humans.
    • Examples:
    • Ascaris lumbricoides (roundworm).
    • Taenia saginata (tapeworm).
    • Taenia solium (tapeworm).
    • Necator americanus (hookworm).
Specific Antihelmintics
  • Drugs for Specific Helminths:
    • Tetrachloroethylene: Treats hookworms.
    • Atabrine: Treats tapeworms.
    • Niclosamide: Treats tapeworms.

Antiprotozoal Drugs

  • Specifically for Plasmodium (malaria):
    • Protozoacidal drugs interfere with the metabolism of the microorganism and inhibit its replication.
    • Examples:
    • Chloroquine: For acute malaria and prophylaxis.
    • Plaquenil: Prophylaxis.
    • Primaquine: Prophylaxis.
    • Daraprim: Acute malaria.
    • Quinine: Acute malaria treatment.
Other Protozoan Infections
  • Entamoeba histolytica (Amebic dysentery): Treatment options include Chloroquine, Paramomycin, Metronidazole, Tetracycline.
  • Giardia lamblia (Dysentery): Treatment includes Metronidazole.
  • Trichomonas (Sexually transmitted disease): Treated with Metronidazole.