Antimicrobial Chemotherapy

Question 1

Streptococcus pyogenes causes

Answer 1

Cellulitis (skin infection) and throat infections

Question 2

Penicillin and all beta lactams are metabolised in the _______ and excreted from the ________ in urine

Answer 2

Liver

Kidney

Question 3

The original penicillin was Penicillin __

Answer 3

Penicillin G - (Benzylpenicillin)

Question 4

How does Penicillin work

Answer 4

Penicillin contains beta lactam ring. They bind on bacteria transpeptidase.
Transpeptidase synthesises bacterial cell wall. So Penicillin inhibits cell wall formation

Question 5

Name one problem of the first penicillin (benzylpenicillin or penicillin G)

Answer 5

Had poor oral bioavailability.
Stomach acid digest it.
Rapid renal clearance

Question 6

Penicillin V was developed after penicillin G, it was orally active and would not be digested by stomach acid. Why was amoxicillin preferred though?

Answer 6

Pen V has a short half live. 6 doses needed a day. Not convenient.
Amoxicillin had a longer half life (twice). Only needed 3 a day

Question 7

Is amoxicillin good for pseudomonas infection ?Y or N

Answer 7

N

Question 8

Give and example of antipseudomonal penicillin

Answer 8

Piperacillin

Question 9

How do bacteria such as S. aureus/E. Coli develop resistance to beta-lactams

Answer 9

By developing beta-lactamase enzymes which hydrolyses beta-lactam rings

Question 10

After resistance development through beta-lactamase enzyme. Name a antibiotic that was produced for staphylococcal beta lactamases infection

Answer 10

Flucloxacillin- the main antibiotic for S. aureus

Question 11

What is the main antibiotics used for S. aureus

Answer 11

Flucloxacillin

Question 12

Name a beta lactamase inhibitor drug

Answer 12

Co-amoxiclav

Produced from amoxicillin + clavulinic acid (protects the antibiotic from degradation)

Question 13

MRSA is resistant to all penicillins. How?

Answer 13

Target alteration/modification mechanism - Mec A gene codes for a different enzyme (not transpeptidase) to synthesise cell wall.
It does not use the beta lactamase enzyme mechanism

Question 14

E. Coli developed resistance to penicillin through 2 mechanism. List them

Answer 14

1. Beta-lactamase enzyme degradation

2. Efflux pumps

Question 15

Mycoplasma/ Chlamydia have always been resistant to penicillin. Why?

Answer 15

They do not possess a cell wall

Question 16

List the 4 mechanisms of antibiotic resistance

Answer 16

1. Alteration of Target site
2. Reducing permeability of cell wall
3. Enzyme degradation
4. Antibiotics Efflux pump

Question 17

Benefits of Cephalosporins antibiotics

Answer 17

Acts against different bacterial species

Its beta-lactam ring does not get hydrolysed by beta-lactamase enzyme

Question 18

Which of the following is not a penicillin
A. Penicillin G
B. Penicillin V
C. Amoxicillin
D. Co-amoxiclav
E. Cephalosporins
F. Flucloxacillin

Answer 18

E. Cephalosporins

Question 19

Streptococcus Pyogenes has not developed resistant to any penicillin, so the best drug is …

Answer 19

Amoxicillin

Question 20

List 5 sites of target for antibiotics. With at least an enzyme of antibiotic that targets that site

Answer 20

1. Cell wall - beta-lactams
2. Protein Synthesis - macrolides/tetracyclines
3. DNA replication- Quinolones
4. RNA synthesis - Rifamycins
5. Antimetabolites- Trimethoprim

Question 21

What antibiotics work on Mycoplasma/chlamydia? and how

Answer 21

Macrolide

Macrolides targets protein synthesis rather than cell wall

Question 22

List 5 reasons why patients might not respond to antibiotic treatment

Answer 22

1. Wrong diagnosis
2. Patient infected with Resistant strain
3. Resistant strain develops after treatment
4. Drug has poor tissue penetration
5. Patient factors: obesity/poor blood supply

Question 23

List 3 issues with antibiotics use

Answer 23

1. Antibiotic allergy is common
2. Antibiotics do not always work, despite expectation to work from lab testings
3. Antibiotics can activates commensals to become opportunistic pathogens

Question 24

Allergy to penicillin is common. True or False

Answer 24

True

Question 25

Amoxicillin
Mechanism of action:
Standard dose:
Adverse effect:
Interactions:

Answer 25

Amoxicillin
- A penicillin
Mechanism of action: inhibition of cell wall synthesis
Standard dose: 250-1000mg 8 hourly
Adverse effect: Allergy, damage to commensal microflora
Interactions: can increase levels of other protein bound drugs

Question 26

Clarythromycin
Mechanism of action:
Standard dose:
Adverse effect:
Interaction:

Answer 26

Clarythromycin:
- A Macrolide. Used when patient are allergic to penicillin and effect against mycoplasma/chlamydia

Mechanism of action: Inhibition of protein synthesis in bacterial ribosome (50s subunit)
Standard dose: 500mg 12 houly
Adverse effect: Nausea and diarrhoea. Arrythmias
Interaction: inhibits enzyme involved in metabolism of other drugs.

Don’t not want to give to patient with lung sclerosis as they wont metabolise it properly

Question 27

Vancomycin
Mechanism of action:
Standard dose:
Adverse effect:
Interaction:

Answer 27

Vancomycin
A Glycopeptide. Active only against Gram positive bacteria. Active against MRSA

Mechanism of action: Inhibits bacterial cell wall (different target to beta-lactams)
Oral bioavailability : very low
Standard dose: 500-1500mg 12 hourly. Narrow therapeutic window
Adverse effect: Toxic to kidney and ears
Interaction: Other drugs