Antibacterial Drugs

Question 1

What should you consider when choosing an antibiotic?

Answer 1

• Effect on bacteria (bactericidal vs static)
• Spectrum of action (narrow vs broad)
• Effect on the patient’s cells
• Route of administration (oral vs injection)
• Duration of action
• Route of excretion/metabolism
• Interactions with other drugs
• Side effects
• Resistance

Question 2

What does bactericidal mean?

Answer 2

It kills the bacteria

Question 3

What does bacteriostatic mean?

Answer 3

prevents the growth of bacteria (stops the bacteria from replicating) - sometimes this is sufficient

Question 4

Why is it sometimes sufficient to have a bacteriostatic antibiotic as opposed to bactericidal one?

Answer 4

It keeps the numbers low and immune system (complement, macrophages and inflammatory mediators can mop up the remaining cells)

Question 5

When should a broad spectrum antibiotic be used?

Answer 5

Active against a wider range of bacteria
- infection that is caused by a mixed group of species OR treating patient in an emergency (we don’t have time to send specimen off to lab for them to tell us what kind of sensitivity bacteria is exhibiting)

Question 6

Why must we be careful when using broad spectrum antibiotics?

Answer 6

It allows bacteria to develop antibiotic resistance as there is no competition from other bacteria present so they can thrive and replicate

Question 7

What is Pseudomembranous colitis? How does it cause damage?

Answer 7

Caused by super infection with bacteria called Clostridium difficile (usually found in the gut - normal gut bug) * Treat pt with antibiotics (particularly broad-spectrum antibiotics: Clindamycin, Amoxicillin) can end up with situation of all bacteria killed in gut, except C difficile which can thrive and replicate.
* Pt can die from destruction of gut wall/pt can end up with sepsis

Question 8

What are broad-spectrum antibiotics?

Answer 8

Amoxicillin
Augmentin (amoxicillin with clavulanic acid)
Tetracycline
Azythromycin

Question 9

What are narrow-spectrum antibiotics?

Answer 9

Penicillin
Metronidazole
Clindamycin
Cephlasporin

Question 10

What toxicity effects should we be aware of?

Answer 10

Autotoxicity, Nephrotoxic and Hepatotoxic

Question 11

Which antibiotic can stain teeth if given when permanent teeth are still developing?

Answer 11

Tetracycline

Question 12

Which drug should be avoided if a patient is on warfarin?

Answer 12

Metronidazole

Question 13

What is the mechanism of action of metronidazole?

Answer 13

Inhibits DNA replication and degrades existing DNA

Question 14

What is the mechanism of action of Tetracycline?

Answer 14

Binds 30s ribosome subunit (inhibit protein synthesis)

Question 15

What is the mechanism of Penicillins?

Answer 15

Inhibit peptidoglycan (murein) cross linking in cell wall

Question 16

What do many bacteria produce making them resistant to penicillins and cephalosporins ?

Answer 16

beta lactamase

Question 17

What can be added to amoxicillin to counteract the resistant bacteria

Answer 17

Clavulanic acid (beta lactamase inhibitor)

Question 18

How do bacteria develop resistance? (5)

Answer 18

• Prevent entry of antibiotic into cell (lots of antibiotics work by preventing DNA replication or protein/RNA synthesis – if antibiotic is stopped from getting into cell, those processes will continue)
• Cleavage of antibiotic structure (eg: beta lactam ring) which will destroy antibiotic and leave it no longer effective
• Alteration of structure of antibiotic (making it unable to enter cell or unable to bind to active site)
• Alter site of action (eg: change shape of target site such as ribosomes, antibiotic can’t work)
• Can be transferred between bacteria and species (not just a matter of bacteria evolving to develop resistance – they can transfer than resistance to another colony – don’t need to be part of same species!)