Antimicrobial Agents

Antimicrobial Agents

Overview of Antibacterial Agents

  • Classification of Antibacterial Agents:
    • Bactericidal Agents:
    • Definition: Agents that kill bacteria.
    • Bacteriostatic Agents:
    • Definition: Agents that inhibit the reproduction and growth of bacteria.
    • Note: The elimination of bacteria is dependent on the phagocytosis by leukocytes and macrophages.

Sources of Antibacterial Drugs

  • Two Main Sources:
    • Microorganisms:
    • Bacteria and other microorganisms produce substances that inhibit the growth of other bacteria.
    • Chemical Synthesis:
    • Drugs are developed through synthesis in laboratories.

Antibiotics and Their Spectrum of Activity

  • **Broad-Spectrum Antibiotics: **
    • Definition: Antibiotics effective against both Gram-positive and Gram-negative bacteria.
    • Example: Penicillin, derived from the fungus Penicillum notatum, inhibits the growth of Gram-positive bacteria.

Penicillins

  • General Characteristics:
    • Classification: Penicillins are bactericidal and interfere with the synthesis of the bacterial cell wall.
    • Generations of Penicillins:
    • First Generation:
      • Effective against Gram-positive bacteria (e.g., streptococci & diplococci).
      • Examples: Penicillin G and Penicillin V.
      • Adverse Effects: Allergies.
    • Second Generation:
      • Effective against both Gram-positive and Gram-negative bacteria, including E. coli, Proteus mirabilis, and Haemophilus influenzae.
      • Examples: Ampicillin and Amoxicillin (broad-spectrum).
      • Combination Example: Amoxicillin + Clavulanic acid = Augmentin (broad-spectrum).
    • Third Generation:
      • Broad-spectrum, utilized against infections from Pseudomonas and Proteus vulgaris.
      • Example: Geocillin.
    • Fourth Generation:
      • More potent than prior generations, used against Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumoniae, and Bacteroides fragilis.
      • Examples: Azlin and Mezlocillin sodium.

Cephalosporins

  • General Characteristics:
    • Bactericidal, with a chemical structure similar to penicillins, interfering with cell wall synthesis.
    • Classified as broad-spectrum antibiotics.
    • Often used in patients allergic to penicillin for the treatment of Gram-negative bacteria.
    • Generations of Cephalosporins:
    • First Generation:
      • Effective against both Gram-positive and Gram-negative infections, and Klebsiella pneumoniae.
      • Examples: Cefadroxil (Duricef) and Cephalexin (Keflex).
    • Second Generation:
      • More potent than the first and primarily used against Gram-negative infections.
      • Examples: Cefaclor (Ceclor) and Cefoxitin (Mefoxin).
    • Third Generation:
      • More potent with longer-lasting effects, used for severe Gram-negative infections.
      • Examples: Cefoperazone (Cefobid) and Cefotaxime (Claforan).

Aminoglycosides

  • General Characteristics:
    • Broad-spectrum bactericidal agents.
    • Mechanism: Inhibit bacterial protein synthesis.
    • Effective against Gram-negative bacilli.
    • Examples: Gentamicin (Garamycin) and Neomycin (Neobiotic).

Tetracyclines

  • General Characteristics:
    • Broad-spectrum antibiotics.
    • Effective against both Gram-positive and Gram-negative bacteria.
    • Mechanism: Interfere with bacterial protein synthesis, acting as bacteriostatic agents.
    • Examples: Tetracycline (Achromycin) and Doxyccline (Vibramycin).
    • Contraindications: Not recommended for pregnant women and children under 7 due to potential effects on tooth development.

Sulfonamides

  • General Characteristics:
    • Effective against both Gram-positive and Gram-negative bacteria.
    • Resistance: Developed over time due to overuse.
    • Current uses: Treatment of urinary tract infections.
    • Examples: Septra, Bactrim, and Silver sulfadiazine (Silvadene).

Other Antibacterial Drugs

  • Isoniazid (INH):
    • Treatment for tuberculosis.
  • Erythromycin (Erythrocin):
    • A macrolide that inhibits bacterial protein synthesis.
    • Used to treat Mycoplasma pneumoniae and chlamydial infections.
  • Chloramphenicol:
    • Broad-spectrum antibiotic used for serious infections such as typhoid fever.
    • Mechanism: Inhibits bacterial protein synthesis, acts as bacteriostatic.

Mechanisms of Action of Antibiotics

  • Synthesis of the Bacterial Cell Wall:
    • Included antibiotics: Beta-lactams (Penicillins, Cephalosporins, Carbapenems, Monobactams, Vancomycin, Bacitracin).
  • Cell Membrane Disruption:
    • Included antibiotics: Polymyxins.
  • Nucleic Acid Synthesis Inhibition:
    • Targeted actions:
    • Dihydropteroate Synthase (PABA).
    • DNA & RNA polymerases.
    • Included antibiotics: Quinolones and Rifampicin.
  • Protein Synthesis Inhibition:
    • Targeted locations:
    • Subunits 50S: Macrolides, Clindamycin, Linezolid, Chloramphenicol.
    • Subunits 30S: Tetracyclines, Aminoglycosides, Streptogramins.

Antifungal Agents

  • Overview:
    • Used to treat diseases caused by fungi (mycosis).
  • Common Antifungal Drugs:
    • Amphotericin B (Fungizone):
    • Used for systemic infections and candidiasis.
    • Clotrimazole (Lotrimin):
    • Effective against Candida albicans infections.
    • Miconazole (Micatin, Monistat):
    • Used against dermatophytic infections and candidiasis.
    • Nystatin:
    • Also treats Candida albicans infections.

Fungal Pathogens and Treatments

  • Types of Fungi:
    • Systemic:
    • Affected areas: Blood, lungs, bones.
    • Example: Histoplasmosis.
    • Treatment: Amphotericin B.
    • Dermatophytes:
    • Affected areas: Skin, hair, nails.
    • Example: Athlete's foot.
    • Treatment: Griseofulvin.
    • Opportunistic Fungi (Candida):
    • Affected areas: Skin, mucosa.
    • Example: Vaginal yeast infection.
    • Treatments include Amphotericin B, Miconazole, and Nystatin.

Classification of Antifungal Drugs

  • By Application:
    • Parenteral:
    • Amphotericin B.
    • Systemic:
    • Oral medications: Griseofulvin, Azoles (including Terbinafine).
    • Topical:
    • Azoles, Nystatin.

Antiviral Agents

  • Overview:
    • Used to combat infections caused by viruses, inhibiting viral replication.
  • Common Antiviral Drugs:
    • Acyclovir (Zovirax): Used to treat herpes simplex.
    • Amantadine, Tamiflu: Used to reduce the severity of influenza.

Classification of Antiviral Drugs

  1. Antiherpesviruses:
    • Nucleoside analogs.
  2. Antigripal:
    • Neuraminidase inhibitors (e.g., Amantadine).
  3. Antiretrovirals:
    • Includes reverse transcriptase inhibitors, protease inhibitors, fusion inhibitors, and interferons.
  4. Others:
    • Ribavirin.

Antihelmintics

  • Overview:
    • Drugs that target parasitic worms infecting humans.
  • Common Pathogens and Treatments:
    • Ascaris lumbricoides (Roundworm).
    • Taenia saginata (Tapeworm).
    • Taenia solium (Tapeworm).
    • Necator americanus (Hookworm).
  • Common Antihelmintics:
    • Tetrachloroethylene (hookworms), Atabrine (tapeworms), Niclosamide (tapeworms).

Antiprotozoal Drugs

  • Overview:
    • Treatment of diseases like malaria caused by protozoa.
    • Mechanism: Protozoacidal drugs interfere with the microorganism's metabolism and inhibit replication.
  • Common Drugs:
    • Chloroquine: Effective against acute malaria, and prophylaxis.
    • Primaquine: Prophylactic for acute malaria.
    • Daraprim (Pyrimethamine): Prophylaxis.
    • Quinine: Effective against acute malaria.

Specific Protozoan Infections and Treatments

  • Entamoeba histolytica: Treatment includes Metronidazole and Tetracycline for amoebic dysentery.
  • Giardia lamblia: Treated with Metronidazole for dysentery.
  • Trichomonas (Sexually transmitted disease): Treatment includes Metronidazole.

Questions and Discussions

  • Open Floor:
    • Address any doubts or questions regarding the material covered.