Microbiology - Antimicrobial Agents 2

Question 1

What mnemonic can be used to help decide which antibiotic to use?

Answer 1

CHAOS
Choice depends on the: 
Host charcteristics 
Antimicrobial susceptibilities of the
Organism itself, as well as the
Site of infection

Question 2

What is the Minimum Inhibitory Concentration and Breakpoint of an antibiotic useful for?

Answer 2

Working out sensitivity
MIC > breakpoint = resistant
MIC < breakpoint = sensitive

Question 3

What antibiotic should be given for gram pos cocci in clusters?

Answer 3

Flucloxacillin

staph aureus

Question 4

What antibiotic should be given empirically for gram neg cocci?

Answer 4

Ceftriaxone (could be meningococcus)

(Neisseria gonorrhoeae), a meningitis (Neisseria meningitidis), and respiratory symptoms (Moraxella catarrhalis, Haemophilus influenzae).

Question 5

What is the “eagle effect”?

Answer 5

Increasing the penicillin dose –> decreasing antibacterial activitity after a point

Question 6

How does the choice of antibiotic to treat UTI differ between community and hospital?

Answer 6

Community: nitrofurantoin/ trimethoprim
Hospital: cephalexin/ augmentin

Question 7

peak influences what and the trough if graph influences what

Answer 7

the peak will influence the dose of the drug given, whereas the trough will determine the frequency

Question 8

give an example of time dependent antibiotics

Answer 8

• Type II (e.g. Penicillins)
o These are time-dependent, so you want to maximise the time above the MIC
o The concentration above the MIC is NOT very important
o So, with penicillins, you tend to take them quite frequently (3-4 times per week)

Question 9

give an example of concentration dependent antibiotics

Answer 9

• Type I (e.g. Aminoglycosides)
o Peak above the MIC (Cmax) is the MOST IMPORTANT factor (these drugs have concentration-dependent effects)
o Therefore, aminoglycosides are given as one big dose once a day, to try and get the Cmax as high as possible
o The higher the Cmax the better the clinical outcome for infections treated with aminoglycosides
o However, achieving high Cmax must be balanced with the risk of adverse effects (ototoxicity and nephrotoxicity)

Question 10

what’s the management of c difficile

Answer 10

• STOP the offending antibiotic (usually a cephalosporin)
• If SEVERE, treat with:
o Metronidazole (PO)
o If above fails, use vancomycin (PO)

Question 11

define MIC

Answer 11

is defined as the lowest concentration of an antimicrobial ingredient or agent that is bacteriostatic (prevents the visible growth of bacteria).