MICRO: Antimicrobial resistance and dosing

Question 1

What are the 4 abx resistance mechanisms?

Answer 1

Enzymatic breakdown
Altered target
Reduced accumulation
Bypassing abx sensitive step

Question 2

Name the MOA of resistance in MRSA.

Answer 2

mecA gene –> PBP2a –> low affinity for beta lactams

Question 3

How is S. pyogenes resistance by PBP alteration overcome?

Answer 3

Increasing dose 
Adding vanc (in pneumo infection)

There is no resistance of S pyogenes (and other strep) to penicillins hence use for tonsillitis

Question 4

Which abx do ESBLs cause resistance to?

Answer 4

Cephalosporins (E coli and klebsiella especially)

Question 5

In which infections is BL production not the MOA of resistance to beta lactams?

Answer 5

MRSA

Pneumococci

Question 6

How do ESBLs spread?

Answer 6

Plasmids or transposons (very fast)

Question 7

What % resistance means you can no longer use the abx?

Answer 7

10%

Question 8

Which gene confers resistance to macrolides?

Answer 8

erm - inducible resistance by using the abx

Question 9

How does the erm gene cause resistance to macrolides?

Answer 9

Altered target - 23S RNA is modified so macrolides less able to bind.

Question 10

What is the resistance MOA of staph aureus to flucloxacillin?

Answer 10

Altered target

NB: flucloxacillin is the only penicillin stable against BLs

Question 11

What is the most common SE of abx in general?

Answer 11

GI upset 
Then:
Fever/rash
Renal 
Anaphylaxis 
Liver

Question 12

Which abx are not absorbed well orally and so given IV?

Answer 12

aminoglycosides

Question 13

Name 2 tests for susceptibility testing.

Answer 13

Gradient MIC method

Agar disc diffusion testing

Question 14

What does the distance from the disc tell you about susceptibility ?

Answer 14

Greater distance means less antibiotic needed (logarithmically)

Question 15

On agar disc diffusion method the …… …. ….. ….. ….. is the MIC.

Answer 15

the border of the clear zone is the MIC

Question 16

How is susceptibility reported by the ECAST?

Answer 16

By break points in a table

If MIC is greater than the break point then the organism is resistant

Question 17

What 3 samples is gram staining useful for?

Answer 17

CSF
Joint aspirate
Pus

Question 18

What are 2 rapid antigen detection tests?

Answer 18

PCR

Immunofluorescence

Question 19

What are the 3 patterns of activity of antimicrobial killing and their goals?

Answer 19

I - concentration-dependent = goal: maximise concentration (peak above MIC)
II - time-dependent = goal: maximise time above MIC
III - time and concentration dependent = goal: maximise amount of drug (AUC)

Question 20

What pattern are aminoglycosides?

Answer 20

I - peak above MIC important

Question 21

How long is osteomyelitis treatment?

Answer 21

6 weeks

Question 22

How long is endocarditis treatment?

Answer 22

4-6 weeks

Question 23

How long is tonsillitis treatment?

Answer 23

10 days

Question 24

What can you give in cellulitis in pen allergic patient?

Answer 24

Vancomycin

Question 25

In addition to abx what is given in invasive GAS?

Answer 25

Early debridement and IVIG

Question 26

What abx does the Eagle effect apply to?

Answer 26

Beta lactams

Question 27

Name 3 atypical CAPs.

Answer 27

Legionella Mycoplasma Chlamydia

Question 28

What is the tx for mild vs severe CAP?

Answer 28

Mild - amox | Severe - co-amox + clarithromycin

Question 29

Name 3 causes of URTIs.

Answer 29

Strep pneumo H influenzae Moraxella

Question 30

What is the tx for HAP?

Answer 30

Cephalosporin + cipro + tazocin | +vancomycin if MRSA

Question 31

What is the tx for hospital-acquired UTI?

Answer 31

Co-amox OR cephalexin

Question 32

What is the tx for infected urinary catheter UTI?

Answer 32

Change catheter under gentamicin cover

Question 33

Which PK/PD is important in beta lactam dosing?

Answer 33

Time above MIC

Question 34

Which PK/PD is important in fluoroquinolone dosing?

Answer 34

Peak above MIC

Question 35

Which PK/PD is important in tetracycline and azithromycin dosing?

Answer 35

AUC

Question 36

Which PK/PD is important in erythromycin dosing?

Answer 36

Time above MIC

Question 37

Which PK/PD is important in glycopeptide dosing?

Answer 37

AUC