MICRO: Antimicrobial resistance and dosing Flashcards
What are the 4 abx resistance mechanisms?
Enzymatic breakdown
Altered target
Reduced accumulation
Bypassing abx sensitive step
Name the MOA of resistance in MRSA.
mecA gene –> PBP2a –> low affinity for beta lactams
How is S. pyogenes resistance by PBP alteration overcome?
Increasing dose Adding vanc (in pneumo infection)
There is no resistance of S pyogenes (and other strep) to penicillins hence use for tonsillitis
Which abx do ESBLs cause resistance to?
Cephalosporins (E coli and klebsiella especially)
In which infections is BL production not the MOA of resistance to beta lactams?
MRSA
Pneumococci
How do ESBLs spread?
Plasmids or transposons (very fast)
What % resistance means you can no longer use the abx?
10%
Which gene confers resistance to macrolides?
erm - inducible resistance by using the abx
How does the erm gene cause resistance to macrolides?
Altered target - 23S RNA is modified so macrolides less able to bind.
What is the resistance MOA of staph aureus to flucloxacillin?
Altered target
NB: flucloxacillin is the only penicillin stable against BLs
What is the most common SE of abx in general?
GI upset Then: Fever/rash Renal Anaphylaxis Liver
Which abx are not absorbed well orally and so given IV?
aminoglycosides
Name 2 tests for susceptibility testing.
Gradient MIC method
Agar disc diffusion testing
What does the distance from the disc tell you about susceptibility ?
Greater distance means less antibiotic needed (logarithmically)
On agar disc diffusion method the …… …. ….. ….. ….. is the MIC.
the border of the clear zone is the MIC
How is susceptibility reported by the ECAST?
By break points in a table
If MIC is greater than the break point then the organism is resistant
What 3 samples is gram staining useful for?
CSF
Joint aspirate
Pus
What are 2 rapid antigen detection tests?
PCR
Immunofluorescence
What are the 3 patterns of activity of antimicrobial killing and their goals?
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)
What pattern are aminoglycosides?
I - peak above MIC important
How long is osteomyelitis treatment?
6 weeks
How long is endocarditis treatment?
4-6 weeks
How long is tonsillitis treatment?
10 days
What can you give in cellulitis in pen allergic patient?
Vancomycin
In addition to abx what is given in invasive GAS?
Early debridement and IVIG
What abx does the Eagle effect apply to?
Beta lactams
Name 3 atypical CAPs.
Legionella
Mycoplasma
Chlamydia
What is the tx for mild vs severe CAP?
Mild - amox
Severe - co-amox + clarithromycin
Name 3 causes of URTIs.
Strep pneumo
H influenzae
Moraxella
What is the tx for HAP?
Cephalosporin + cipro + tazocin
+vancomycin if MRSA
What is the tx for hospital-acquired UTI?
Co-amox OR cephalexin
What is the tx for infected urinary catheter UTI?
Change catheter under gentamicin cover
Which PK/PD is important in beta lactam dosing?
Time above MIC
Which PK/PD is important in fluoroquinolone dosing?
Peak above MIC
Which PK/PD is important in tetracycline and azithromycin dosing?
AUC
Which PK/PD is important in erythromycin dosing?
Time above MIC
Which PK/PD is important in glycopeptide dosing?
AUC
