antimicrobial chemotherapy

Question 1

What was the original penicillin?

Answer 1

benzylpenicillin (penicillin G)

Question 2

How do penicillins work?

Answer 2

by binding bacterial transpeptidases, inhibiting cell wall formation

Question 3

What is the functional unit in penicillin?

Answer 3

beta lactam ring

Question 4

Which penicillin is naturally occuring?

Answer 4

benzylpenicillin (penicillin G)

Question 5

Describe benzylpenicillin (penicillin G)

Answer 5

• poor oral bioavailibility
• rapid renal clearance, requires frequent dosing

Question 6

Which penicillins are chemically modified penicillins?

Answer 6

• phenoxymethulpenicillin (pen V)
• amonipenicillins (e.g amoxicillin)

Question 7

What is amoxicillin used against?

Answer 7

• S. pyogenes infections (sore throat, skin infections)
• pneumococcal infections (respiratory tract)
• susceptible E.coli infections (UTIs)

Question 8

What is amoxicillins mechanism of action?

Answer 8

inhibition of bacterial cell wall synthesis

Question 9

What is the standard dose for amoxicillin?

Answer 9

250-1000mg 8 hourly

Question 10

What are some adverse effects of amoxicillin?

Answer 10

• allergy
• damage to commensal microflora

Question 11

How is amoxicillin excreted?

Answer 11

urine

Question 12

What are the mechanisms of resistance against amoxicillin?

Answer 12

• primarily enzymatic degradation
• target modification (e.g MRSA strains)
• efflux in some gram negatives

Question 13

What is amoxicillins half life?

Answer 13

an hour

Question 14

What are some interactions that amoxicillin can have?

Answer 14

can increase levels of other protein bound drugs

Question 15

How is Staphylococcus aureus resistant to penicillin?

Answer 15

encode penicillinases which hydrolyse the beta-lactam ring

Question 16

What were the first antibiotics developed to target the penicillin resistant strains of S. aureus?

Answer 16

• methicillin (not used clinically, only as a lab test)
• flucloxacillin (now the main one used)

Question 17

What is co-amoxiclav?

Answer 17

amoxicillin plus clavulinic acid

Question 18

How are MRSA strains now resistant to all beta-lactam antibiotics?

Answer 18

• target modification (modified transpeptidase enzyme)
• encoded by mecA gene

Question 19

Why are mycoplasmas and chlamydias resistant to penicillin?

Answer 19

as they have no cell walls

Question 20

How are most gram negative bacteria resistant to penicillin?

Answer 20

• most make beta lactamases
• develop resistance through other mechanisms like antibiotic efflux pumps

Question 21

What are the 4 main ways bacteria become resistant to antibiotics?

Answer 21

• enzymatic degradation of the drug
• target modification
• efflux of antibiotic from bacteria
• reduced penetration through cell wall

Question 22

What are some antibiotic sites of action?

Answer 22

• cell wall
• protein synthesis
• DNA replication
• RNA synthesis
• antimetabolites

Question 23

What is the most common pathogen causing cellulitis?

Answer 23

Streptococcus pyogenes

Question 24

What is clarythromycin?

Answer 24

a macrolide

Question 25

What is clarythromycin used for?

Answer 25

used in patients that have a penicillin allergy - S. pyrogenes infection (sore throat, skin infections) - pneumococcal infections (respiratory tract) - gram -ve infections such as haemophilus influenzae (respiratory tract)

Question 26

What is clarythromycin's mechanism of actions?

Answer 26

inhibition of protein synthesis in the bacterial ribosome (50S subunit)

Question 27

What is clarythromycin's standard dose?

Answer 27

500mg 12 hourly

Question 28

What is clarythromycin's half life?

Answer 28

1-6 hours

Question 29

How is clarythromycin excreted?

Answer 29

metabolites in bile

Question 30

What are the adverse effects on clarythromycin?

Answer 30

- nausea and diarrhoea - may alter cardiac conduction, arrythmias

Question 31

Which interactions can clarythromycin have?

Answer 31

inhibits enzymes (cytochrome p450 enzymes) involved in he metabolism of other drugs

Question 32

What are the methods of resistance against clarythromycin?

Answer 32

primarily mutational target modification

Question 33

What is vancomycin?

Answer 33

a glycopeptide

Question 34

What is vancomycin active against?

Answer 34

- gram +ve bacteria - many resistant strains including methicillin resistant S. aureus (MRSA)

Question 35

What is vancomycin's method of action?

Answer 35

inhibits bacterial cell wall formation by a different target to beta lactams

Question 36

What is vancomycins method of resistance?

Answer 36

- target modification - cell wall thickening, reduced penetration

Question 37

What is the standard dose for vancomycin?

Answer 37

500-1500mg 12 hourly - narrow therapeutic window, levels needed to kill bacteria are close to levels that are toxic to patients

Question 38

What is vancomycin's half life?

Answer 38

4-8 hours

Question 39

What is vancomycins oral bioavailability?

Answer 39

very low

Question 40

How is vancomycin excreted?

Answer 40

urine

Question 41

What are some adverse effects of vancomycin?

Answer 41

- nephrotoxic - ototoxic

Question 42

What are some of the interactions that vancomycin has?

Answer 42

with any other nephrotoxic or ototoxic drugs