Lecture Notes: Antimicrobial Drugs

Question of the Day

• Stages of Phage Infection:
  1. Attachment: Phage binds to bacterial cell.
  2. Entry: Viral DNA enters the bacterial cell.
  3. Synthesis: Bacteriophage parts are synthesized.
  4. Assembly: Assembly of bacteriophage parts.
  5. Release: New phages released by cell lysis.

History of Antimicrobial Drugs

• Quinine:
  • Extracted from Cinchona tree bark.
  • Used for treatment of malaria.
• Paul Ehrlich's Magic Bullet:
  • Developed Salvarsan for syphilis treatment.
  • Basis for chemotherapy.
• Gerhard Domagk:
  • Developed first sulfa drug, Prontosil.
  • Awarded (but declined) Nobel Prize in 1939.
• Alexander Fleming:
  • Discovered penicillin in 1929.
  • Observed inhibition of Staphylococcus aureus by Penicillium mold.
• Chain and Florey:
  • Purified penicillin and conducted clinical trials.

Sources of Antibiotics

• Soil-Derived Antimicrobials:
  • Streptomyces, spore-forming organisms, and molds like Penicillium.

Definitions

• Chemotherapeutic Agents: Kill cancer cells.
• Selective Toxicity: Targets harmful microorganisms without damaging the host.
• Synthetic Drugs: Lab-made, non-organic origins.
• Semi-synthetic Drugs: Natural products chemically modified to improve efficacy, reduce side effects, and expand treatment range.

Antimicrobial Drugs Features

• Selective Toxicity: Key feature in drug design.
• Bacteriostatic vs. Bactericidal:
  • Bacteriostatic: Stops bacteria growth without killing.
  • Bactericidal: Kills bacteria.
• Spectrum of Activity:
  • Broad-Spectrum: Effective against wide range (e.g., gram-positive and gram-negative).
  • Narrow-Spectrum: Effective against specific bacteria type.
• Tissue Distribution and Metabolism:
  • Consider drug half-life and distribution.

Drug Combinations

• Synergistic Effects: Drugs enhance each other (e.g., codeine and acetaminophen).
• Antagonistic Effects: Drugs counteract (e.g., penicillin and tetracycline).

Adverse Effects

• Allergies: Common in patients.
• Toxicity: Potential side effects.
• Suppression of Normal Flora:
  • Can lead to diarrhea, yeast infections.

Microbial Resistance

• Intrinsic vs. Acquired Resistance:
  • Intrinsic: No effect on the microbe.
  • Acquired: Due to mutation or genetic element (e.g., plasmids).
• Mechanisms of Resistance:
  1. Inactivation of Antibiotic.
  2. Alteration of Target Site.
  3. Decreased Uptake.
  4. Increased Elimination.

Emerging Antimicrobial Resistance

• Resistant Bacteria Examples:
  • Vancomycin-resistant Enterococci.
  • Methicillin-resistant Staphylococcus aureus (MRSA).
  • Streptococcus pneumoniae.
  • Multi-drug-resistant Mycobacterium tuberculosis.

Prevention and Control

• Role of Physicians:
  • Prescribing practices and patient education.
• Role of Patients:
  • Follow instructions, complete course.
• Public Awareness:
  • Understand limitations of antibiotics.

This concludes today's lecture on antimicrobial drugs.