Antimicrobials 2

Question 1

What are examples of adverse events in 5% of hospitalised patients?

Answer 1

GI upset
Fever and rash 
Renal dysfunction 
Acute anaphylaxis 
Hepatitis

Question 2

What does the the choice of abx depend on?

Answer 2

Host characteristics- pregnant, young, elderly, renal failure
Antimicrobial susceptibilities of the-often unknown, most empiric
Organism itself
Site of infection

Question 3

What influences choice of drug?

Answer 3

Pharmacokinetics eg clindamycin good for abcesses but doesn’t get into CNS
Route of admin
Dosage

Question 4

What should the choice of drug ideally be?

Answer 4

Narrow spectrum
Bactericidal- bacteraeima eg lactam or glycosides 
Based upon bacterial diagnosis 
Local sensitivity patterns 
Cost

Question 5

What is the minimum inhibitory concentration?

Answer 5

Least amount of drug required to inhibit the organism in vitro
At this breakpoint, if mic is less than that it’s sensitive, above its resistance
Resistance is a continuum

Question 6

How does the agar diffusion method work?

Answer 6

Abx impregnated disc absorbs moisture from the agar, abx diffuses into the agar medium
Distance from disc increases, there is a logarithmic reduction in abx
Diffused abx at interface of growing and inhibited bacteria is MIC

Question 7

What do you do if you need to treat on an empirical basis?

Answer 7

Use broad spectrum- especially septic patients, then de-escalate, shift from initially using narrow.
No tx equals efficacy of abx but no other tx affects society at large
Collect specimen for culture
Then change empirical cover to narrow

Question 8

What does identification of infecting organism involve?

Answer 8

Gram stain
Rapid antigen detection. Use IF for organisms that are hard to grow eg PCP.
Don’t use PCR so widely- doesn’t give sensitivities

Question 9

What affects site of infection and thus local conc of abx?

Answer 9

pH at infection site eg low ph deactivate aminiglycosides. tigecytin good for tissue bad for blood
Clinda for strep but not urinary excretion so bad for group b UTI. poor choice
Lipid solubility of drug
Ability to penetrate BBB
Endocarditis, bactercidal is impt

Question 10

What is evidence of a systemic response?

Answer 10

Fever
Raised CRP
increased WBC or decreased
Duration of symptoms, underlying risk factors, likely source of infection

Question 11

What are issues with route of admin?

Answer 11

Cephalosporin- poor oral absorption
IM- not for long term, avoid if bleeding tendency
Topical don’t have systemic side fx
Recommend switch to po after iv

Question 12

What pharmacokinetic factor effects glycosides?

Answer 12

Gentamicin has rapid bacericidal effect which is influenced by peak above MIC, greater clinical outcome. Aminiglycosides have post abc effect, so when curve goes under mic, it still has effect. Peak is important, once daily dosing

Question 13

What pharmacokinetic factor effects pencillin?

Answer 13

The time above the MIC ie exposure. Amount isn’t impt, need frequent doses. Infusion would be good

Question 14

What pharmacokinetic factor effects vancomycin?

Answer 14

Conc and time above is impt eg area under curve

Question 15

What abx needs maximum concentration?

Answer 15

Amino
Daptomycin
Fluoroquinonlones
Jet oldies

Question 16

Which abx need maximum duration?

Answer 16

Carbapenems
Cephalosporin 
Erythomycin
Linezolid
Pencillin

Question 17

Which abx need maximum amount of drug?

Answer 17

Azithromycin
Clindamycin 
Oxazolidinones 
Tetracycline 
Vancomycin

Question 18

What are a few of the recommended tx courses for particular infections?

Answer 18

N meningitis- 7 days 
Acute osteomyelitis- 6 weeks
Bacterial endocarditis- 4-6 weeks 
Gp A strep pharyngitis-10 days 
Simple cystitis- 3 days

Question 19

What should you use for skin infections eg impetigo, cellulitis, wound infections?

Answer 19

Flucloxacillin, unless MRSA/allergic use clarithromycin or clindamycin

Question 20

What is used in severe skin infections?

Answer 20

Aggressive and early debridement- group a strep
Adjunctive use of protein synthesis inhibitors esp clindamycin, bacteria in stationary cycle of division.
Use of IVig

Question 21

What is the eagle effect?

Answer 21

Originally referred to reduced antibacterial effect of pencillin at high doses, recently refers to lack of efficacy of beta lactam antibacterial drugs on infections having large number of bacteria

Question 22

What is the mechanism of the eagle effect?

Answer 22

In cases of high bacterial burden, bacteria may be in stationary phase of growth, due to nutrient restriction.
So pencillin has no activity, only works on rapidly dividing cells.

Question 23

Which bacteria are covered by pencillin in resp tract infection?

Answer 23

Haemophilus and pneumococci

Question 24

What is given in severe pneumonia?

Answer 24

Co amox - lots of haemophilus produce b lactamase

Question 25

What is given for atypical pneumonia?

Answer 25

Clar- mycoplasma, legionella

Question 26

What cause HAI pneumonia?

Answer 26

Gram neg
Give cephalosporin, ciprofloxacin or tazocin
If MRSA colonised, consider adding vanco

Question 27

What do you give in bacterial meningitis?

Answer 27

Strep pneumo or n meningitis

Ceft +/- amox if listeria likely

Question 28

What do you use in baby under 3 months for meningitis?

Answer 28

Cefotaxime plus amox
Don’t give ceftriaxone, displaced bilirubin from albumin and can cause biliary sludging
NM- benzypencillin or ceft

Question 29

How is resistance caused in nm pencillin?

Answer 29

Production of altered PBPA

Treatment may still be affected with higher dose of pencillin

Question 30

How do you treat c diff?

Answer 30

Treat with metro oral

If fails, use vanco oral

Question 31

How is misuse of antimicrobial agents common?

Answer 31

No infection present
Selection of incorrect drug
Inadequate or excessive dose
Inappropriate duration of therapy 
Expensive agent used when cheaper is available