Antibiotics and Resistance

Question 1

How do antibiotics work?

Answer 1

Bacteriostatic - stop the reproduction and growth of bacteria

Bactericidal - kill bacteria directly

Question 2

List antibiotics that inhibit cell wall synthesis

Answer 2

With a beta-lactam ring:
Penicillin
Carbapenems such as meropenem
Cephalosporins

Without a beta-lactam ring:
Vancomycin
Teicoplanin

Question 3

List antibiotics that inhibit folic acid metabolism

Answer 3

Sulfamethoxazole blocks the conversion of PABA to DHFA

Trimethoprim blocks the conversion of DHFA to THFA

Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim

Question 4

What is metronidazole used for and why?

Answer 4

Used for anaerobes

Reduction of metronidazole into its active form only occurs in anaerobic cells

When partially reduced metronidazole inhibits nucleic acid synthesis

Question 5

List antibiotics that inhibit protein synthesis by targeting the ribosome

Answer 5

Macrolides such as erythromycin, clarithromycin and azithromycin

Clindamycin

Tetracyclines such as doxycycline

Gentamicin

Chloramphenicol

Question 6

Basic stepwise approach to antibiotic cover

Answer 6

Start with amoxicillin which covers streptococcus, listeria and enterococcus

Switch to co-amoxiclav to additionally cover staphylococcus, haemophilus and e. coli

Switch to tazocin to additionally cover pseudomonas

Switch to meropenem to additionally cover ESBLs

Add teicoplanin or vancomycin to cover MRSA

Add clarithromycin or doxycycline to cover atypical bacteria