Antibiotics

Question 1

What is Natural Antagonism?

How are Antibiotics derived from these Natural products?

Answer 1

• Natural products of pathogens that helps kill/inhibit growth of other microbes to give them a selective advantage
• By Fermentation, then modified to ↑Pharmacological and Antimicrobial properties

Question 2

Selective Toxicity:
What’s it due to?

How do Antibiotics affect the Commensal Flora? What can this lead to? Give an example

What is the Therapeutic Index?
→ What is this like for Toxic drugs?

Answer 2

• Differences in structure and metabolic pathways between a host and pathogen
• Loss of Commensal Flora = Bacterial overgrowth e.g. Pseudomembranous (Antibiotic-associated) Colitis
• Range between when the dose has a therapeutic effect and a toxic effect
  → Narrow Range

Question 3

Antibiotic Classification:
What does Bactericidal mean? When is it used?

What does Bacteriostatic mean? When is it used?

What’s the difference between a Broad and Narrow Spectrum Antibiotic?

What's the structure of most Antibiotics?
→ Give an example of a class that does this

Answer 3

• KILLS bacteria - Used when host defense mechanisms are impaired e.g. Endocarditis, Kidney infections
• INHIBITS bacteria - Used when host defense mechanisms are still intact
• • Broad-spectrum - Effective against many types
  • Narrow-spectrum - Effective against few types
• Mimic the structure of natural substrates for bacterial enzymes
  → β-lactam antibiotics (Penicillin and Cephalosporins)

Question 4

What are the ways in which Antibiotics target Bacteria? Give examples of drugs

How does it affect Cell wall synthesis?
→ Which type of bacteria is this more effective in?
→ How does Penicillin produce these effects?

How does it affect Protein Synthesis?

What are the 2 things Antibiotics can be used for?

Answer 4

• • Inhibit Cell wall synthesis (e.g. β-lactams, Vancomycin)
  • Inhibit Protein synthesis (e.g. Erythromycin, Tetracycline, Streptomycin) - binds to bacterial ribosomes
  • Inhibit DNA and RNA
  • Inhibit Folic acid metabolism
  • Damage cell membrane
  • Produce free radicals in bacteria (e.g. Metronidazole)
• Inhibits Peptidoglycan production in the cell wall
  → Much easier in Gram-positive than Gram-negative bacteria
  → Penicillin (β-lactam) enters and binds to PBP (Penicillin-binding protein/Transpeptidase) to stop the production of Peptidoglycans
• Binds and changes shape of bacterial ribosomes, causing misreading of mRNA
• Treatment and Prophylaxis

Question 5

What determines which Antibiotic is used?

What are the routes in which Antibiotics can be given?

Why are Antibiotics combined for treatment?

Answer 5

• • Distribution in body
  • Spectrum of activity, Toxicity, Renal function, Patient’s clinical condition (stable/unstable)
  • Type of bacteria and its antibiotic sensitivity
• Oral, IV, Topical
• • Polymicrobial infections
  • Synergistic effects e.g. Penicillin + Gentamicin
  • Reduce antibiotic resistance

Question 6

Antibiotic Therapy:
Stage 1 - What’s the patient’s condition? How would you manage them?

Stage 2 - What’s the patient’s condition? How would you manage them?

Stage 1 - What’s the patient’s condition? How would you manage them?

Answer 6

• Unstable - Give Broad-spectrum antibiotic
• Stabilising (Pathogen/site identified) - Rationalise therapy and give Narrow-spectrum antibiotic
• Stable - Discharge with Oral antibiotics