Antimicrobial Agents

Question 1

How can you classify the different antimicrobial agents?

Answer 1

• Inhibition of cell wall synthesis
• Inhibition of protein synthesis
• Inhibition of DNA synthesis
• Inhibition of RNA synthesis
• Inhibition of folate metabolism
• Cell membrane toxicity

Question 2

What are the classes of drugs that inhibit cell wall synthesis? Give some examples of each

Give examples of bacteria these target

Answer 2

Beta lactams:
- Penicillin (gram positive bacteria)

Cephalosporins:
- Ceftriaxone (gram negative bacteria)

Carbapenems:
- Meropenem (gram negative bacteria)

Glycopeptides:
- Vancomycin (MRSA, c. diff)

Question 3

What are the classes of drugs that inhibit protein synthesis? Give some examples of each

Give examples of bacteria these target

Answer 3

Aminoglycosides
- Gentamicin (gram negative sepsis)

Tetracyclines
- Doxycycline (intracellular bacteria - chlamydia)

Macrolides
- Erythromycin (gram positive bacteria, for PCN allergy)

Chloramphenicol
- Used in eye infections

Oxazolidinones
- Linezolid (gram positive bacteria, MRSA and VRE)

Question 4

What are the classes of drugs that inhibit DNA synthesis? Give some examples of each

Give examples of bacteria these target

Answer 4

Fluoroquinolones
- Ciprofloxacin (gram negative bacteria)

Nitroimidazoles
- Metronidazole (anaerobes and protozoa)

Question 5

What are the classes of drugs that inhibit RNA synthesis? Give some examples of each

Give examples of bacteria these target

Answer 5

Rifamycin

- Rifampicin (mycobacterium)

Question 6

What are the classes of drugs that inhibit folate metabolism? Give some examples of each

Give examples of bacteria these target

Answer 6

Sulphonamides
- Sulphamethoxazole (PCP, with trimethoprim co-trimoxazole)

Diaminopyrimidines
- Trimethoprim (UTIs)

Question 7

Give some examples of broad spectrum antimicrobials

Answer 7

• Co-amoxiclav
• Tazocin
• Ciprofloxacin
• Meropenem

Question 8

Give some examples of narrow spectrum antimicrobials

Answer 8

• Flucloxacillin
• Metronidazole
• Gentamicin

Question 9

What are the classes of drugs that are toxic to the cell membrane? Give some examples of each

Give examples of bacteria these target

Answer 9

Polymyxin
- Colistin (gram negative bacteria)

Cyclic lipopeptide
- Daptomycin (gram positive bacteria, MRSA, VRE)

Question 10

What are the mechanisms of antimicrobial resistance?

Answer 10

BEAT

1) Bypass antibiotic-sensitive pathway
2) Enzyme mediated drug inactivation
3) Impairment of drug accumulation
4) Modification of drug target on microbe

Question 11

What is a common organism to cause infection in the skin? So what antimicrobial is usually used?

Answer 11

Staph. aureus

Flucloxacillin

Use local guidelines

Question 12

What is a common organism to cause infection in the pharynx? So what antimicrobial is usually used?

Answer 12

Beta-haemolytic streptococcus

Benzylpenicillin

Use local guidelines

Question 13

What is a common organism to cause infection in the lungs (community)? So what antimicrobial is usually used?

Answer 13

Pneumococcus or haemophilus

Mild: amoxicillin

Severe: co-amoxiclav + clarithromycin

Use local guidelines

Question 14

What is a common organism to cause infection in the lungs (hospital)? So what antimicrobial is usually used?

Answer 14

Gram negative bacteria

Use amoxicillin + gentamicin
Or tazocin

Use local guidelines

Question 15

What is a common organism to cause infection in the CNS? So what antimicrobial is usually used?

Answer 15

Meningococcus or streptococcus

Ceftriaxone (+amoxicillin if listeria is likely - young/old/immunocompromised)

Use local guidelines

Question 16

What is a common organism to cause infection in the urethra? So what antimicrobial is usually used?

Answer 16

E. Coli

Community: Trimethoprim

Nosocomial: co-amoxiclav or cephalexin

Use local guidelines

Question 17

What is a common organism to cause sepsis? So what antimicrobial is usually used?

Answer 17

Severe: tazocin or ceftriaxone or metronidazole + gentamicin

Neutropaenic: tazocin + gentamicin

Use local guidelines

Question 18

What is a common organism to cause infection in the colon? So what antimicrobial is usually used?

Answer 18

Clostridium difficile

Metronidazole PO

Use local guidelines