Infectious Diseases

Question 1

What are the mechanisms of action of the antiviral drugs used to treat CMV?

Answer 1

1) Ganciclovir/Valganciclovir (Valgan better bioavailability)
- guanosine analogues that inhibit UL54 (CMV polymerase). Gets phosphorylated by UL97
2) Foscarnet
- pyrophosphate analogue that directly binds to UL54
3) Cidofovir
- cytosine analogue inhibits UL54
4) Marabivir
- targets viral UL97

Question 2

What is the most common causative organism of cellulitis?

Answer 2

Beta haemolytic streptococcus

Question 3

What is the treatment for uncomplicated erysipelas?

Answer 3

Oral penicillin

Question 4

What pharmacodynamic principals apply to microbial killing with amino glycosides?

Answer 4

Concentration dependent killing
Cmax/MIC
(Max concentration/minimum inhibitory concentration)

Need to aim for highest concentration possible to get good killing, and minimal duration of high doses to prevent toxicity (toxicity based on AUC)

Question 5

What is the mechanism of resistance of ESBL organisms?

Answer 5

Extended spectrum beta-lactamases

Enzyme mediated resistance - hydrolysed beta lactam molecule (the efficacious part of the antibiotic)

Gives resistance to all penicillins, cephalosporins and aztreonam

Most common plasmid is the CTX-M gene

Question 6

How can you differentiate ESBL resistance from ampC?

Answer 6

AmpC resistant to cefoxitin, ESBL susceptible in vitro

AmpC is an inducible chromosomal gene, ESBL is plasmid mediated

AmpC not inhibited by beta lactamase inhibitors eg clavulanic acid, ESBL is in the lab

Question 7

What antibiotics to choose for ESBL?

Answer 7

Carbapenems
Gentamicin if susceptible
Amikacin