Microbiology 3 - 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 characteristics (are they pregnant, are they a child, do they have seizures, are they allergic)
Antimicrobial susceptibilities of the
1. Organism itself, as well as the
2. Site of infection

Additionally:
FOLLOW LOCAL GUIDELINES
Consider pharmacokinetics, route of administration, dosage (age + weight, renal/hepatic function)

Question 2

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

Answer 2

Working out sensitivity

MIC = minimum drug concentration required to inhibit the growth of an organism in culture

Compare the MIC with a standard breakpoint (level of therapy where the antibiotic is associated with clinical success)

MIC > breakpoint = resistant
MIC < breakpoint = sensitive

Question 3

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

Answer 3

Flucloxacillin

Question 4

What antibiotic should be given empirically for gram neg cocci?

Answer 4

Ceftriaxone (could be meningococcus)

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

What is empirical and definitive therapy?

Answer 7

Empiric therapy is treating the patient using our best guess - based on differential diagnosis and local guidelines

Definitive therapy is commenced once culture results are received

TAKE CULTURE SAMPLES BEFORE STARTING EMPIRIC THERAPY - to prevent results from being affected

Question 8

Once you know an organism’s susceptibility, should you switch their antibiotics?

Answer 8

Based on susceptibility, try to de-escalate to the narrowest spectrum antibiotic possible -> reduces side-effects, reduces likelihood of C. diff growth, reduces alterations to gut flora etc.