MicrobiologyBytes: Infection & Immunity: Antimicrobials Updated: August 23, 2007 Search

Antimicrobial Chemotherapy

Aims and Objectives

After reading this document, you should:

  1. Know the common drugs used to treat bacterial infections
  2. Know the common drugs used to treat viral infections
  3. Know the common drugs used to treat fungal infections
  4. Know the common drugs used to treat protozoal infections
  5. Know the mechanisms of action of the common antibacterial agents
  6. Know the mechanisms of action of the common antiviral agents
  7. Know the mechanisms of action of the common antifungal agents
  8. Know the mechanisms of action of the common antiprotozoal agents
  9. Know the principles of use of common antibacterial agents
  10. Know the mechanisms of resistance to common antibacterial agents

Principles of Antimicrobial Chemotherapy

The ideal antimicrobial agents are selective in that they will target the micro-organism but not the cell. In practice, there is a therapeutic index where there is differential activity between the action on the microbe and the effect (toxicity) on the host. Bacteria are prokaryotes with different life systems to man and are easier to target than the other agents.

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Common Antibacterial Agents

Class of Drug Examples Mechanism of Action Uses
Penicillins Benzylpenicillin Amoxycillin Piperacillin Flucloxicillin Inhibit cell wall synthesis Streptococcal, meningococcal, pneumococcal infections
Cephalosporins Cephradine Cefotaxime Ceftazidime Inhibit cell wall synthesis Respiratory and urinary infections
Monobactams Aztreonam Inhibit cell wall synthesis Pseudomonas
Aminoglycosides Gentamycin Netilmicin Amikacin Inhibit protein synthesis gram-negative coliform infections
Tetracyclines Oxytetracycline Minocycline Inhibit protein synthesis Chlamydial and mycoplasmal infections
Chloramphenicol   Inhibit protein synthesis Second-line for Salmonella and Haemophilus influenzae infections
Macrolides Erythromycin, Azithromycin Inhibit protein synthesis Gram-positive cocci, Legionella, Chlamydia
Quinolones Ciprofloxacin Sparfloxacin Inhibit DNA gyrase Pseudomonas
Sulphonamides Sulphamethoxazole Compete with para-aminobenzoic acid In co-trimoxazole
Nitroimidazoles Metronidazole Inhibit nucleic acid synthesis Anaerobic infections
Vancomycin   Inhibit cell wall synthesis MRSA

Common Antiviral Drugs

Drug Uses Mechanism Of Action
Acyclovir, famciclovir, valaciclovir Herpesviruses Nucleoside analogue
Ganciclovir Cytomegalovirus Nucleoside analogue
Azidothymidine HIV Nucleoside analogue
Ribavirin RS virus Nucleoside analogue
Amantadine, rimantadine Influenza A Inhibit virus uncoating and assembly
Nevirapine HIV Protease inhibitor
Viruses use host cell machinery and are therefore very difficult to target.

Common Antifungal Agents

Drug: Uses: Mechanism of Action:
Amphotericin B Systemic fungal infections Alters permeabilization of cell membrane
Azoles e.g. Clotrimazole, miconazole, fluconazole Local candidosis and dermatophyte infections. Systemic fungal infections Inhibit sterol synthesis
Flucytosine Serious fungal infections Competes with uracil
Antifungal agents tend to have a low therapeutic index and are rapidly destroyed by cellular enzymes.

Common Antiprotozoal Agents

Drug Uses Mechanism of Action
Imidazoles, e.g. metronidazole, tinidazole Entamoeba, Giardia, Trichomonas Interferes with several metabolic pathways
Pyrimethamine Malaria, toxoplasma Inhibits folic acid reduction
Pentamidine Pneumocystis, Trypanosoma rhodesiense/gambiense Inhibits aerobic glycolysis
Chloroquine, quinine Malaria Inhibits nucleic acid synthesis

© AJC 2007.