Abx Susceptibility

Question 1

What is an MIC?

Answer 1

(Minimum inhibitory concentration → lowest concentration of drug that completely inhibits growth of the bacteria)

Question 2

Can you use a drug who’s breakpoint MIC is below that of the MIC of a bacteria?

Answer 2

(No, the breakpoint MIC needs to be above the MIC of the bacteria)

Question 3

Do you want to MIC 90 of a bacteria to be high or low?

Answer 3

(Low)

Question 4

What does susceptible mean on a susceptibility report?

Answer 4

(Treatment of this bacteria with this antibiotic has a high likelihood of therapeutic success = bacterial MIC is less than or equal to breakpoint MIC)

Question 5

What does intermediate mean on a susceptibility report?

Answer 5

(Therapeutic effect is uncertain, may have efficacy in body sites where the drugs are physiologically concentrated)

Question 6

What does resistant mean on a susceptibility report?

Answer 6

(Treatment of this bacteria with this antibiotic has high likelihood of therapeutic failure = bacterial MIC is greater than or equal to breakpoint MIC)

Question 7

What are some examples of when susceptibility testing can overestimate true susceptibility?

Answer 7

(When the infection is intracellular and/or when it is an infection of a protected site (eye, prostate, CNS))

Question 8

What value should you look for on a susceptibility report to indicate a Staphylococcus pseudintermedius is resistant?

Answer 8

(Oxacillin resistance)

Question 9

(T/F) You should be extra worried when a Staph pseudintermedius is also resistant to imipenem.

Answer 9

(Not really, imipenem is a beta lactam so if your Staph pseud is beta lactamase producing, of course imipenem isn’t going to work)

Question 10

If you have a bacteria that is resistant to cefpodoxime and you suspect it is an extra spectrum beta lactamase producing Enterobacterales, what other information would make it even more likely?

Answer 10

(If it is susceptible to clavamox (something with a beta lactamase inhibitor))

Question 11

What is Pseudomonas intrinsically resistant to?

Answer 11

(Penicillins, most cephalosporins, tetracyclines, chloramphenicol, TMS, easily develops resistance to fluoroquinolones)

Question 12

Enterococcus has intrinsic resistance to which antibiotics?

Answer 12

(Aminoglycosides (alone), cephalosporins, clindamycin, and TMS (tho may appear S in vitro))

Question 13

What is ceftazidime equivalent to in vet med?

Answer 13

(Cefpodoxime)

Question 14

Why is cephalothin equivalent to cephalexin but not cefazolin?

Answer 14

(Because cefazolin is given IV and has a wider spectrum compared to cephalexin so cephalothin may underestimate cefazolins activity)

Question 15

(T/F) If something is susceptible to tetracycline, it is likely susceptible to doxycycline and minocycline.

Answer 15

(T, also means if something is not susceptible to tetracyclines it may still be susceptible to doxy/mino)

Question 16

(T/F) If something is susceptible to erythromycin, it is likely susceptible to azithromycin and clarithromycin.

Answer 16

(T, also means if something is not susceptible to erythromycin it may still be susceptible to azithro/clarithro)

Question 17

What is the main concern with shortening the dosing interval of chloramphenicol?

Answer 17

(It may lead to drug accumulation → toxicity and more inhibition of other drugs)