10. Antimicrobial Agents

Question 1

List common Antibacterials with examples

Answer 1

• Penicillins (flucloxacillin, amoxycillin)
• Cephalosporins (cephalexin
• Carbapenems (meropenem, ertapenem)
• Tetracyclines (doxycycline)

Question 2

Mechanism of action for antibacterials

Answer 2

1. Inhibit bacterial cell wall synthesis (bactericidal affect)
   o Contents of bacteria are under high osmotic pressure so their variability depends on integrity of cell walls
   o Inhibition of cell wall synthesis weakens it and causes cell to lyse
2. Disrupting or altering membrane permeability (bacteriostatic/bactericidal effect)
   o Results in leakage of essential bacterial metabolic substrates
3. Inhibiting bacterial proteins synthesis (bacteriostatic/bactericidal effect)
   o Some agents induce formation of defective protein molecules (bactericidal)
   o Some inhibit specific steps of protein synthesis (bacteriostatic)
4. Inhibiting synthesis of essential metabolites (bacteriostatic effect)
   o Act as competitive inhibitors of enzymes in metabolic pathway

Question 3

Selecting an antimicrobial agent (AMA)

Answer 3

Antimicrobials: static (inhibitory), cidal (lethal), ie;

• Bacteriostatic inhibits spread of infection by suppressing growth and replication of bacteria – eg. Chloramphenicol against Staphylococcus Aureas
• Bactericidal kills the bacteria – eg. Penicillin

Question 4

Types of AMA treatments

Answer 4

Types of AMA treatments

• Empirical treatment: based on treating most likely pathogen, ABX given before identifying pathogen
• Microbiology guided treatment: antimicrobials prescribed after pathogen is identified
• Prophylactic treatment: administration of ABX to prevent future infection

Question 5

Patient factors

Answer 5

• Immune system
• Renal dysfunction
  o Poor function causes accumulation of ABX which would otherwise be eliminated
  o Some AMA are nephrotoxic eg. Aminoglycosides
• Hepatic dysfunction
  o Eg. Erythromycin and tetracycline are concentrated or eliminated by the liver
• Poor perfusion  decreased circulation of ABX to infection site
• Age
  o Neonates vulnerable to toxicity of chloramphenicol due to poor renal and hepatic elimination process
• Pregnancy
  o Many ABX cross placenta

Question 6

Safety

Answer 6

ie. penicillin least toxic, chloramphenicol less microorganism specific and thus reserved for serious infections