Classification of Antimicrobial Drugs

Chemotherapeutic Agents and Antimicrobial Drugs

• Chemotherapeutic agents are chemical agents that combat disease in the body.
• Antimicrobial drugs are chemical agents that destroy microorganisms, and may be synthetic or natural.

Classification of Antimicrobial Drugs

• Classified according to spectrum of activity:
  • Broad spectrum antibiotics: act against both gram negative and gram positive bacteria (e.g. amoxicillin, ciprofloxacin)
  • Narrow spectrum antibiotics: act against certain microorganisms (e.g. penicillin)
• Classified according to mechanism of action:
  • Drugs acting on cell wall (e.g. penicillin)
  • Drugs acting on protein synthesis (e.g. aminoglycosides)
  • Drugs acting on cell membrane (e.g. polymyxin)
  • Drugs acting on nucleic acid biosynthesis (e.g. rifampicin)
• Classified according to bactericidal or bacteriostatic activity:
  • Bactericidal: eliminate bacteria (e.g. aminoglycosides)
  • Bacteriostatic: inhibit growth of bacteria (e.g. chloramphenicol)

Action of Antimicrobial Drugs

• Directly kill microorganisms (bactericidal)
• Inhibit growth of microorganisms (bacteriostatic)

Mechanism of Action

• Inhibition of cell wall synthesis (e.g. cephalosporins, penicillins, vancomycin)
• Inhibition of cell membrane function (e.g. clostin, polymyxin B)
• Inhibition of protein synthesis (e.g. chloramphenicol, erythromycin, clindamycin, tetracyclines, aminoglycosides)
• Inhibition of nucleic acid synthesis (e.g. quinolones, rifampin, sulfonamides, trimethoprim)

Mechanisms of Drug Resistance

• Microorganisms produce enzymes that destroy the activity of the drug
• Microorganisms develop an altered metabolic pathway that bypasses the reaction inhibited by the drug
• Microorganisms develop an altered enzyme

Origins of Drug Resistance

• Non-genetic origin:
  • Active replication of bacteria is required for most antibacterial drug action
  • Microorganisms may lose specific target structure and become resistant
  • Intracellular microorganisms are not affected by drugs as long as they stay inside cells
• Genetic origin:
  • Chromosomal mutation: develops as a result of spontaneous mutation in a locus that controls susceptibility to a given drug
  • Extrachromosomal "plasmid mediated resistance": carries genes for resistance to one or several antimicrobial drugs
  • R-factor composed of two parts: resistant-transfer factor (RTF) and R-determinant
  • Dissemination by bacterial conjugation mainly
  • Genetic material and plasmid can be transferred by transformation, transduction, and conjugation

Chemotherapeutic Agents and Antimicrobial Drugs

• Chemotherapeutic agents are chemical agents that combat disease in the body.
• Antimicrobial drugs are chemical agents that destroy microorganisms, and may be synthetic or natural.

Classification of Antimicrobial Drugs

• Classified according to spectrum of activity:
  • Broad spectrum antibiotics: act against both gram negative and gram positive bacteria (e.g. amoxicillin, ciprofloxacin)
  • Narrow spectrum antibiotics: act against certain microorganisms (e.g. penicillin)
• Classified according to mechanism of action:
  • Drugs acting on cell wall (e.g. penicillin)
  • Drugs acting on protein synthesis (e.g. aminoglycosides)
  • Drugs acting on cell membrane (e.g. polymyxin)
  • Drugs acting on nucleic acid biosynthesis (e.g. rifampicin)
• Classified according to bactericidal or bacteriostatic activity:
  • Bactericidal: eliminate bacteria (e.g. aminoglycosides)
  • Bacteriostatic: inhibit growth of bacteria (e.g. chloramphenicol)

Action of Antimicrobial Drugs

• Directly kill microorganisms (bactericidal)
• Inhibit growth of microorganisms (bacteriostatic)

Mechanism of Action

• Inhibition of cell wall synthesis (e.g. cephalosporins, penicillins, vancomycin)
• Inhibition of cell membrane function (e.g. clostin, polymyxin B)
• Inhibition of protein synthesis (e.g. chloramphenicol, erythromycin, clindamycin, tetracyclines, aminoglycosides)
• Inhibition of nucleic acid synthesis (e.g. quinolones, rifampin, sulfonamides, trimethoprim)

Mechanisms of Drug Resistance

• Microorganisms produce enzymes that destroy the activity of the drug
• Microorganisms develop an altered metabolic pathway that bypasses the reaction inhibited by the drug
• Microorganisms develop an altered enzyme

Origins of Drug Resistance

• Non-genetic origin:
  • Active replication of bacteria is required for most antibacterial drug action
  • Microorganisms may lose specific target structure and become resistant
  • Intracellular microorganisms are not affected by drugs as long as they stay inside cells
• Genetic origin:
  • Chromosomal mutation: develops as a result of spontaneous mutation in a locus that controls susceptibility to a given drug
  • Extrachromosomal "plasmid mediated resistance": carries genes for resistance to one or several antimicrobial drugs
  • R-factor composed of two parts: resistant-transfer factor (RTF) and R-determinant
  • Dissemination by bacterial conjugation mainly
  • Genetic material and plasmid can be transferred by transformation, transduction, and conjugation