Antimicrobials Made Simple: Mechanism, Resistance, and Smart Usage

 Antimicrobials Made Simple: Mechanism, Resistance, and Smart Usage

SECTION 1 – GENERAL PRINCIPLES OF CHEMOTHERAPY

• Chemotherapy: Use of chemical agents to selectively harm pathogenic organisms without harming the host.
• Selective toxicity (Key principle).

Memory tip: “SELECT”

• Selective toxicity
• Efficacy
• Low resistance potential
• Economical
• Compatibility with host
• Target-specific

Historical message:
Paul Ehrlich (1909) – “Magic bullet” concept → Salvarsan for syphilis.

SECTION 2 – MECHANISM OF ACTION OF ANTIMICROBIALS

Slide 4 – Main Targets

1. Cell wall synthesis inhibitors – β-lactams, vancomycin.
2. Protein synthesis inhibitors – aminoglycosides, tetracyclines, macrolides.
3. Nucleic acid synthesis inhibitors – fluoroquinolones, rifampicin.
4. Metabolic pathway inhibitors – sulfonamides, trimethoprim.
5. Cell membrane disruptors – polymyxins, amphotericin B.

Memory tip: “Can People Not Make Cell walls?”
(C – Cell wall, P – Protein, N – Nucleic acid, M – Metabolism, C – Cell membrane)

SECTION 3 – FACTORS AFFECTING SELECTION & USE

Key Factors

• Site of infection (BBB penetration for meningitis)
• Patient factors (age, pregnancy, renal/hepatic function)
• Drug factors (spectrum, toxicity, cost, route)
• Pathogen factors (susceptibility, resistance pattern)

Memory tip: “SPaD” – Site, Patient, Drug.

SECTION 4 – RATIONALE OF COMBINATION THERAPY

Why Combine?

• Broaden spectrum (empirical therapy)
• Synergistic effect (e.g., penicillin + gentamicin)
• Prevent resistance (e.g., TB therapy)
• Reduce toxicity (lower doses of each drug)

Caution: Antagonism possible (bacteriostatic + bactericidal in some cases).

Memory tip: “BSPaR” – Broaden, Synergize, Prevent resistance, Reduce toxicity.

SECTION 5 – CLASSIFICATION OF ANTIMICROBIALS

By Target

• Antibacterial – β-lactams, aminoglycosides, tetracyclines…
• Antiviral – acyclovir, oseltamivir…
• Antifungal – azoles, echinocandins…
• Antiprotozoal – metronidazole, chloroquine…

By Spectrum

• Narrow (penicillin G) vs broad (tetracycline).

SECTION 6 – MECHANISM OF RESISTANCE

How Bacteria Resist

1. Enzymatic degradation (β-lactamase).
2. Altered target site (MRSA’s altered PBP).
3. Efflux pumps.
4. Reduced permeability.
5. Bypass pathways.

Memory tip: “EAT PB” – Enzyme, Alter target, efflux Transport, Permeability, Bypass.

Historical Milestones

• 1928 – Fleming discovers penicillin.
• 1940s – Widespread antibiotic use; WWII survival rates soar.
• 1950s–70s – Golden age of antibiotic discovery.
• Present – Crisis of antimicrobial resistance.

Message: “We stand on the shoulders of discoverers; our job is to preserve their gift by using antimicrobials wisely.”

Conclusion

• Antimicrobials are powerful but must be used rationally.
• Understand mechanisms, selection factors, combinations, and resistance to guide safe therapy.

                                              END OF THE DOCUMENT

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