M9: CC2: Practical Aspects of Antibiotic Therapy Flashcards Preview

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Flashcards in M9: CC2: Practical Aspects of Antibiotic Therapy Deck (28)
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1
Q

What different types of antibiotic prescribing are there?

Prophylaxis is the use of _ agents to _

Types (4)

A

antimicrobial
prevent infection

perioperative
endocarditis
travel
opportunistic infection

2
Q

What different types of antibiotic prescribing are there?

Perioperative prophylaxis is used to prevent _ infections

Clean wound:
No _ encountered
_, _, and _ not entered

Clean-contaminated wound:
_, _, or _ entered without significant _

Contaminated wound:
Gross spillage from _
Entrance into _ or _ with infected _ or _
Traumatic wounds or any wound with _

A

surgical site

inflammation
Respiratory, GI and GU tract

GI, GU or respiratory tracts
spillage

GI tract
GU or biliary tract, urine or bile
pus

3
Q

What different types of antibiotic prescribing are there?

Endocarditis prophylaxis is used to prevent _ (infections of _) with procedures that induce _

Travel prophylaxis may be taken by travelers to prevent _

Opportunistic infection prophylaxis may be taken by _ patients to prevent infections such as _

A

endocarditis
heart valves
bacteremia

malaria

immunocompromised 
Pneumocystis jiroveci (carinii)
4
Q

What different types of antibiotic prescribing are there?

Pre-emptive therapy is the use of antibiotics in case of an _ infection which is likely to become _ with serious consequences unless treated.

The treatment decision is mostly based on _.

ex. Starting _ in a transplant patient with evidence of _ reactivation by increased viral load per PCR in serum

A

asymptomatic
symptomatic

laboratory markers

valganciclovir
cytomegalovirus (CMV)

5
Q

What different types of antibiotic prescribing are there?

Empiric therapy is the use of antibiotics for a _ infection but before the _ of the infection is known

Common infections for which empiric therapy is given include fever in _ patients, _-acquired pneumonia and _-associated pneumonia.

In general, delaying the antibiotic therapy until the microbiological diagnosis is made can be (beneficial / detrimental) to the patient in case of a rapidly progressing infection

The antibiotics chosen for empiric therapy depend on individual patient factors, exposures and local epidemiology

Empiric antibiotic therapy is by necessity “(broad / narrow)” in many instances

In some suspected infections it may be better to wait for _ or _ rather than give empiric antibiotics.

Many infections resolve due to the _ and do not justify the use of antibiotics.

A

presumed
etiology

neutropenic
community
ventilator

detrimental

broad

clinical progress or the results of cultures and susceptibilities

immune system of the host

6
Q

What different types of antibiotic prescribing are there?

Pathogen-directed therapy is when the organism is _, but antibiotic susceptibility is _

Appropriate antibiotics can be selected based on the local _ of antimicrobial susceptibility, but are (broader / narrower) than when the susceptibility of the infecting organism is known.

A

known
awaited

epidemiology
broader

7
Q

What different types of antibiotic prescribing are there?

Susceptibility-guided therapy is when the organism and the antibiotic susceptibility are both _

This allows for “_” of antibiotic therapy.

In general the antibiotic with the (broadest / narrowest) spectrum, the most _, least _ and _ is chosen.

A

known

streamlining

narrowest
effective
toxic
cheapest

8
Q

On which occasions are no antibiotics required?

_ (for example, rhinitis) for which no effective antimicrobial medications exist.

_ (for example, one of two sets of blood cultures with coagulase-negative staphylococci)

_ (for example, the finding of vancomycin resistant Enterococcus faecium from a rectal swab)

_ (for example, bronchitis) even if bacteria are the cause.

Also, adequate _ obviates the need for antibiotics

A

Suspected viral infection

Contamination of the sample

Colonization in the absence of infection

Treatment has not shown to hasten the resolution of the infection

surgical drainage of an abscess

9
Q

How do microbiology laboratories perform antibiotic susceptibility testing?
Disk diffusion:

Disks containing _ are placed on an agar plate and _ of bacterial growth is measured.

The greater the zone, the more _.

Method which determines the MIC? (y/n)

A

antibiotics
zone of inhibition

susceptible the bacteria are to the antibiotics diffused from the disk

n

10
Q

How do microbiology laboratories perform antibiotic susceptibility testing?
Broth macrodilution, microdilution and agar dilution:

Test-tubes, microtiter plates or agar plates containing varying _ of the antibiotic are inoculated with the organism.

These are the classic methods for determining the _ of the antibiotic against that particular organism.

This is the lowest concentration of antibiotic at which there is _

Method which determines the MIC? (y/n)

A

concentrations

minimum inhibitory concentration (MIC)

no visible growth in the test-tube

y

11
Q

How do microbiology laboratories perform antibiotic susceptibility testing?
E-test:

A _ is impregnated with different concentrations of antibiotics along its gradient.

The strip is placed directly on an _ inoculated with the organism.

The zone of inhibition can be read as the _

Method which determines the MIC? (y/n)

A

patented strip

agar plate

MIC

y

12
Q

How do microbiology laboratories perform antibiotic susceptibility testing?
Commercial semi-automated methods:

These have a small number of _ containing varying concentrations of the antibiotic to be tested.

Usually only the concentrations around the “breakpoint” differentiating _ from _ organisms are tested.

Method which determines the MIC? (y/n)

A

wells

susceptible
resistant

n

13
Q

How do microbiology laboratories perform antibiotic susceptibility testing?
Genetic testing:

PCR amplification can identify the presence of _ (rifampin resistant TB) or _ encoding enzymes conferring resistance to antimicrobials (HIV genotyping).

Method which determines the MIC? (y/n)

A

antimicrobial resistance genes

mutations in genes

n

14
Q

What are some of the pharmacodynamic considerations in prescribing antibiotics?

2 types of antibiotics

A

concentration-dependent

time-dependent

15
Q

What are some of the pharmacodynamic considerations in prescribing antibiotics?
Concentration-dependent antibiotics:

  • Achieve maximal efficacy at _
  • The upper concentration limit in the patient is limited by the concentrations that will produce _

(Examples include _ and _)

  • Knowledge of the MIC is important because the ratio of _ to MIC is a predictor of efficacy of _
A

maximal concentrations

toxicity

aminoglycosides
fluoroquinolones

peak concentration
aminoglycosides

16
Q

What are some of the pharmacodynamic considerations in prescribing antibiotics?
Time-dependent antibiotics:

  • Do not result in better efficacy at concentrations of more than _
  • The time the concentration of drug at the site of infection _ is the major determinant of clinical efficacy

(Examples include _ and _)

  • Continuous _ or multiple _ optimizes the time above the MIC
A

4 times the MIC

exceeds the MIC

beta-lactams
vancomycin

infusion
daily doses

17
Q

What are other determinants in choosing antibiotics?
Route of administration:

Most antibiotics are available in _ form. This is especially helpful if the patient is too sick or if the _ system is not capable of _ the antibiotic.

Some antibiotics are absorbed very well and the intravenous formulation can be exchanged to an _ if the patient has improved

(Examples include _, _, and _).

A

intravenous
gastro-intestinal
absorbing

oral pill

azithromycin
trimethoprim-sulfamethoxazole
fluoroquinolones

18
Q

What are other determinants in choosing antibiotics?
Anatomic site where the infection needs treatment:

Most IV antibiotics reach sufficient levels in the _, so bacteremias are treatable as long as the drug levels exceed the _ of the bacteria.

However, due to the _ it is very difficult for antibiotics to reach adequate levels in the _ compartment and high doses need to be used.

Also, antibiotics may not reach adequate concentrations in _ and other poorly _ sites (foreign materials implanted, necrotic bone).

A

blood stream
MIC

blood-brain barrier
cerebrospinal

pus (abscess)
perfused

19
Q

What are other determinants in choosing antibiotics?
Combination therapy:

Used as _, when a wide range of organisms are suspected, that cannot be covered by _. Ex. _.

Used for _, when the efficacy of a combination is expected to be more than the summation of the efficacy of each antibiotic alone. Ex.Enterococcal endocarditis where a combination of _ and _ is more efficacious than either agent alone.

To prevent emergence of _. Ex. _ therapy for active tuberculosis, which combines _, _, _, and _. Another example is _ for which 3 active drugs must be used simultaneously to attain durable viral suppression.

A

empiric therapy
monotherapy
Bacterial meninigitis

synergy
ampicillin and gentamicin

resistance
Induction
rifampin, isoniazid, pyrazinamide and ethambutol (RIPE)
HIV

20
Q

What are other determinants in choosing antibiotics?
Toxicity:

(Aminoglycosides / Cephalosporins) are more toxic (nephrotoxic, ototoxic) than (Aminoglycosides / Cephalosporins).

As soon as the causative _ is identified and _ are determined you should use the least toxic drug.

A

Aminoglycosides
cephalosporins

micro-organism
susceptibilities

21
Q

What are other determinants in choosing antibiotics?
Costs:

(Linezolid / Nafcillin) is much cheaper than (Linezolid / Nafcillin) so the latter should only be used in specific circumstances justifying the much higher costs.

A

Nafcillin

linezolid

22
Q

Example of the interpretation of MIC’s in treatment of Streptococcus pneumoniae:

PCN MIC ≤2 µg/ml is reported as (susceptible / intermediate / resistant) (92% at PUH):

Treat with IV _ 18 million units/24 hours

A

susceptible

Penicillin

23
Q

Example of the interpretation of MIC’s in treatment of Streptococcus pneumoniae:

PCN MIC =4 µg/ml is reported as (susceptible / intermediate / resistant) (5% PUH):

Treat with IV _ 24 million units/24 hours or _

Higher dose of _ (PCN or ceftriaxone) overcome the resistance mediated by PCN binding proteins (PBPs)

There is no benefit of adding _ (clavunalate, sulbactam, tazobactam) since the resistance to beta-lactams is due to _ and not beta-lactamases.

A

intermediate

Penicillin
Ceftriaxone

beta-lactams

beta-lactamase inhibitors
PBPs

24
Q

Example of the interpretation of MIC’s in treatment of Streptococcus pneumoniae:

PCN MIC ≥8 µg/ml is reported as (susceptible / intermediate / resistant) (3% PUH):

Treat with _

Even very high doses of _ (PCN or ceftriaxone) cannot overcome the PBP mediated resistance.

There is no benefit of adding _ (clavunalate, sulbactam, tazobactam) since the resistance to beta-lactams is due to _ and not beta-lactamases.

A

resistant

Vancomycin

beta-lactams

beta-lactamase inhibitors
PBPs

25
Q

Example of the interpretation of MIC’s in treatment of Streptococcus pneumoniae:

These new PCN MIC breakpoints for the interpretation of susceptibilities of Streptococcus pneumoniae are NOT applicable for _ due to the blood brain barrier.

PCN has lower achievable concentrations in _ than in other compartments and although in theory a Streptococcus pneumoniae isolate with MIC=4 from _ (reported as resistant) could be treated with high dose _ alone, additional highly dosed _ is required.

A

meningitis

cerebrospinal fluid
CSF
beta-lactams
vancomycin

26
Q

Example of the interpretation of MIC’s in treatment of Streptococcus pneumoniae:

1) The MIC of bacteria such as Strep pneumo for a certain antimicrobial can be determined by _ or by _.

The higher the MIC, the higher the _.

2) The MIC itself is not affected by the _ from where the bacteria is isolated.
3) However, the interpretation of the MIC calling the bacteria susceptible, intermediate or resistant to an antimicrobial is dependent upon the .
4) So if the MIC of a bacterium is lower than the concentration attained by the antimicrobial in the infected compartment, we call it “
.”

A

broth dilution
Etest

concentration of that antimicrobial is required to inhibit its growth

location /body site

compartment from where the isolate is obtained i.e. the location of the infection

resistant

27
Q

Example:

A certain E.coli strain isolated has a MIC of 32 for cefepime. A safe IV dose of cefepime attains a serum level of 25 and a urine level of 100.

So if the E. coli was isolated from blood (bacteremia) it was reported as _ to cefepime.

But if the E. coli was isolated from urine (in case of bladder infection) it could have been reported as _ to cefepime.

A

resistant

susceptible

28
Q

Example:

Strep pneumoniae isolated has a MIC of 1 for PCN. A safe IV dose of PCN attains a serum level of 30 and CSF level of 0.5

So if the Strep pneumo was isolated from blood it was reported as _ to PCN.

But if the Strep pneumo was isolated from CSF (case of meningitis) it was reported as _ to PCN.

A

susceptible

resistant