Antimicrobial Drugs and Antibiotics

Antimicrobial Drugs

• Antimicrobial drugs treat microbial infections.
• Antibiotics kill or inhibit bacterial growth, treating bacterial infections.

Antibiotics

• Fight pathogens
• Interfere with cell wall formation
• Many are obtained from bacteria or fungi
• Others are synthesized

History of Antibiotics

• The first antibiotic's discovery was accidental.
• In 1928, Alexander Fleming, a Scottish biologist, accidentally contaminated a petri dish with a fungus.
• He observed a clear area of no bacterial growth where the fungus contaminated the plate.

Zone of Inhibition

• If an antibiotic stops bacterial growth or kills bacteria, a clear zone forms around the antibiotic disk where no bacterial growth occurs.
• Factors affecting zone size include:
  • Drug diffusion rate
  • Drug concentration
  • Type of microorganism
  • Type of drug

Narrow and Broad-Spectrum Antibiotics

• Narrow-spectrum: Affect specific microbes (e.g., gram-positive cells).
  • Examples: Clarithromycin, Clindamycin, Erythromycin
  • Advantages: Less likely to harm normal body microbes, reducing the risk of superinfection. So, only use if the causative organism is known.
• Broad-spectrum: Affect a wide range of microbes.
  • Examples: Azithromycin, Amoxicillin, Vancomycin, Levofloxacin, Streptomycin, Tetracycline, Chloramphenicol
  • Disadvantages: Can harm normal body microbes, increasing the risk of superinfection. Also, can lead to drug resistance.
  • Children receiving broad-spectrum in the first year of life may increase risk of developing childhood asthma.

Antibiotic Targets

• Bacterial cell wall
• Bacterial plasma membrane
• Bacterial protein synthesis
• Bacterial nucleic acids
• Bacterial metabolism

Inhibitors of Cell Wall Synthesis

• Penicillins contain a beta-lactam ring.
• Natural penicillins, produced by Penicillium, are effective against gram-positive bacteria.

Inhibitors of Protein Synthesis

• Aminoglycosides, tetracyclines, chloramphenicol, and macrolides inhibit protein synthesis at 70S ribosomes.

Inhibitors of Nucleic Acid Synthesis

• Rifamycin inhibits mRNA synthesis, used to treat tuberculosis.
• Quinolones and fluoroquinolones inhibit DNA gyrase, used to treat urinary tract infections.

Antibiotic Resistance

• Resistance can be inherent or acquired.
• Inherent: Some bacteria are naturally resistant due to physiological characteristics.
• Acquired: Bacteria acquire resistance through the transfer of resistance genes or spontaneous chromosomal mutations.

Mechanisms of Antibiotic Resistance

• Production of enzymes (e.g., beta-lactamases, aminoglycoside-modifying enzymes, chloramphenicol acetyl transferase).
• Mutation, altering proteins like PBPs.
• Efflux pumps, removing antibiotics from bacteria.

Allergy Testing

• Used to identify substances causing allergic reactions.
• Methods: Skin prick test and batch test.

Antifungal Drugs

• Used to treat and prevent fungal infections (mycoses).
• Types: Polyenes, Imidazoles, Triazoles, Allylamines, Inhibitors.

Antiretroviral Drugs

• Classified into five groups, targeting specific viral processes:
  • NRTIs (Nucleoside/Nucleotide Reverse Transcriptase Inhibitors)
  • NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors)
  • Protease Inhibitors
  • Entry Inhibitors
  • Integrase Inhibitors

Antiprotozoan and Antihelminthic Drugs

• Chloroquine and quinacrine stop DNA synthesis by intercalation.
• Metronidazole treats a wide variety of bacterial and parasitic infections by stopping growth.
• Niclosamide treats cestodes, parasites infecting humans and animals.