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PT 1 > L20, 21 Introduction to Antibiotics > Flashcards

L20, 21 Introduction to Antibiotics Flashcards

1
Q

Appropriate antibiotic therapy depends on what factors?

A
  1. Knowledge/suspicion of the site of infection and subsequent infecting pathogen (where/what)
  2. Spectrum of activity of the antibiotic
  3. Host characteristics
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2
Q

True or false - it does not matter when you obtain a culture from a patient.

A

False - obtain cultures from the suspected site before antibiotics are initiated.

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3
Q

True or false - isolation of an organism from a clinical specimen does not always indicate the presence of infection.

A

True

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4
Q

What are the four possibilities when an organism is detected in culture?

A
  1. Normal flora
  2. Contamination
  3. Colonization
  4. Infection
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5
Q

What happens to a patient’s flora within 48 hours of admission?

A

They are colonized with “new flora” (usually gram-negative aerobes)

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6
Q

Why do normal flora suppress the growth of pathogenic bacteria?

A

They colonize sites that might be otherwise colonized by pathogenic bacteria.

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7
Q

What are the 7 sterile body sites and the fluids found in each?

A
  1. Bloodstream (blood)
  2. Subarachnoid space (CSF)
  3. Pleural space (pleural fluid)
  4. Peritoneum (peritoneal fluid)
  5. Pericardiam (pericardial fluid)
  6. Synovium (synovial fluid)
  7. Urinary tract (urine - directly from bladder)
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8
Q

What is contamination and a common example?

A

Organism inadvertently introduced into the specimen during collection or processing; coagulase negative staph in the blood of the patient

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9
Q

What is colonization and a common example?

A

Organism is present at a body site but is not invading host tissue or invading signs and symptoms of infection; pseudomonas aeruginosa in the sputum of a patient without signs of pneumonia

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10
Q

What is infection and a common example?

A

Pathogenic organism is damaging host tissue and eliciting signs and symptoms of infection; S. pneumoniae in the sputum of a patient with fever, productive cough, and shortness of breath

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11
Q

Certain bacteria have a propensity to commonly cause infection in particular ___. Give 2 examples.

A

Body sites or fluid; E. coli in the urine and S. aureus in skin abscesses

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12
Q

What information can help choose an antibiotic before the results of a culture are available?

A
  1. Site of infection
  2. Likely causative organism
  3. Gram-stain result
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13
Q

Why are antibiotics initiated when an infection is suspected but not confirmed?

A

Undue delay may lead to significant morbidity or mortality

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14
Q

What is the difference between empiric and direct/targeted therapy?

A

Empiric is chosen based on activity against likely pathogens; direct/targeted is modified once culture and susceptibility results are available

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15
Q

What is the antimicrobial spectrum of activity?

A

General list of bacteria that are killed or inhibited by an antibiotic; established during early clinical trials

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16
Q

What type of antibiotic has activity against a limited group of bacteria?

A

Narrow spectrum

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17
Q

What type of antibiotic has activity against a wide variety of bacteria?

A

Broad spectrum

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18
Q

___ testing is performed on individual bacterial isolates once grown and identified in culture.

A

Antibiotic susceptibility

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19
Q

What is the MIC (minimum inhibitory concentration)?

A

Lowest concentration of an antibiotic that inhibits visible bacterial growth

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20
Q

What is the MBC (minimum bactericidal concentration)?

A

Lowest concentration of an antibiotic that kills bacteria (decreases inoculum by 99.9%)

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21
Q

What are interpretive guidelines established by the CLSI that categorize specific antibiotic MIC values for a given bacteria?

A

Susceptibility breakpoints

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22
Q

What are the 3 susceptibility breakpoints and what do they mean?

A
  1. Susceptible: organism will most likely be eradicated with normal doses of the antibiotic
  2. Intermediate: treatment may be successful using maximal doses of the antibiotic
  3. Resistant: MIC exceeds usual serum concentrations of the antibiotic, so less than optimal results are expected
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23
Q

Why do S, I, and R vary for each antibiotic and each bacteria?

A

They are based on the PK of the drug, general activity of the antibiotic, site of infection, and data from clinical efficacy trials.

24
Q

In general, can MIC values be compared between different antibiotics?

A

No

25
Q

What are the two major methods for MIC determination and how do they work, generally?

A
  1. Macrodilution
  2. Microdilution

Two-fold serial dilutions of the antibiotic in broth are incubated with a standard inoculum of the infecting bacteria

26
Q

In a broth dilution, what is the MIC?

A

The lowest concentration of antibiotic that prevents visible growth of the bacteria (first tube without visible growth)

27
Q

How does a macrodilution differ from a microdilution?

A

A macrodilution involves test tubes with dilutions of one antibiotic; a microdilution involves microtiter plates or cassettes with serial dilutions of several antibiotics

28
Q

Which type of dilution yields the exact MIC of the antibiotic?

A

Macrodilution

29
Q

What does MBC do?

A

Extends the macrodilution test and represents the antibiotic concentration that kills the bacteria

30
Q

What is a qualitative test of the in vitro activity of an antibiotic (MIC not determined)?

A

Disk diffusion (Kirby Bauer)

31
Q

What test combines the quantitative benefits of broth dilution with the ease of disk diffusion and yields an MIC? Where is the MIC?

A

E-test; where the ellipse crosses the strip

32
Q

What is included in a hospital antibiogram?

A

Susceptibility data for the most common bacteria isolated in the hospital annually

33
Q

What type of therapy decreases the emergence of resistance?

A

Combination therapy

34
Q

What is it called when the activity of the antimicrobial combination is greater than expected from the additive activity of the individual antibiotics?

A

Synergy combination therapy

35
Q

What is it called when the activity of the combination is no greater than the sum of the effects of each individual agent?

A

Additive combination therapy

36
Q

What is it called when the activity of the combination is less than expected from the additive activity of the individual agents?

A

Antagonistic combination therapy

37
Q

What type of antibiotic inhibits bacteria growth? What does killing depend on?

A

Bacteriostatic; the host defense mechanisms

38
Q

What are the disadvantages of bacteriostatic antibiotic therapy?

A

In the setting of inadequate host defenses, any partially inhibited organisms may survive, replicate, and produce recurrent infection when the antibiotic is discontinued (or serum concentrations fall below MIC)

39
Q

What are 8 examples of bacteriostatic antibiotics?

A
  1. Macrolides
  2. Ketolides
  3. Tetracyclines
  4. Glycylcyclines
  5. Sulfonamides
  6. Clindamycin
  7. Synercid
  8. Linezolid
40
Q

What type of antibiotic kills bacteria?

A

Bactericidal

41
Q

What are bactericidal antibiotics preferred? When are they required?

A

Preferred: immunocompromised

Required: endocarditis, osteomyelitis, febrile neutropenia

42
Q

What are 10 examples of bactericidal antibiotics?

A
  1. Penicillins
  2. Cephalosporins
  3. Carbapenems
  4. Aztreonam
  5. Fluoroquinolones
  6. Aminoglycosides
  7. Vancomycin
  8. Daptomycin
  9. Bactrim
  10. Metronidazole
43
Q

Which categories of antibiotics are bactericidal? Which are bacteriostatic?

A

Bactericidal: cell wall synthesis inhibitors, nucleic acid synthesis inhibitors, metabolic inhibitors

Bacteriostatic: protein synthesis inhibitors

44
Q

PK/PD looks at the ___ vs. ___.

A

Effect; time

45
Q

What is the PAE (post-antibiotic effect)?

A

The time it takes for a bacteria to regrow once serum concentrations of the antibiotic have dropped below the MIC; it is specific to the drug and organism

46
Q

Agents with ___ (long/short) PAEs can be dosed to allow serum concentrations to fall below the MIC.

A

Long

47
Q

Describe the PAE of Gram-positive bacteria.

A

All antibiotics have some PAE; 2 hours for beta-lactams

48
Q

Describe the PAE of Gram-negative bacteria.

A

Prolonged PAEs with protein or nucleic acid synthesis inhibitors such as aminoglycosides and fluoroquinolones

49
Q

The higher the concentration, the ___ (greater/lesser) the killing. This is concentration-dependent killing.

A

Greater

50
Q

Describe time dependent killing.

A

In time-dependent killing, the killing depends on the time of exposure above the MIC, not on the serum concentration.

51
Q

Changing the ___ can extend the time of infusion to improve time dependent killing.

A

Rate of infusion

52
Q

What are the 5 general steps to anti-microbial selection?

A
  1. Confirm presence of infection
  2. Select empiric therapy
  3. Identify pathogen
  4. Modify antibiotic therapy
  5. Monitor therapeutic response
53
Q

What are the 3 infection-specific parameters to consider when choosing an antibiotic?

A
  1. Severity of infection (affects route of administration, dose, # of antibiotics)
  2. Site of infection
  3. Infecting organism
54
Q

What are the 6 host factors to consider when choosing an antibiotic?

A
  1. Allergies
  2. Age
  3. Pregnancy or nursing
  4. Renal/hepatic function
  5. Concomitant drug therapy
  6. Underlying disease states
55
Q

Which 7 antibiotics are primarily eliminated by the kidneys?

A
  1. Most beta-lactams
  2. Vancomycin
  3. Aminoglycosides
  4. Some FQs
  5. Bactrim
  6. Daptomycin
  7. Tetracyclin
56
Q

Which 9 antibiotics are eliminated by the liver?

A
  1. Macrolides
  2. Synercid
  3. Linezolid
  4. Clindamycin
  5. Metronidazole
  6. Some FQs
  7. Bactrim
  8. Doxycycline
  9. Tigecycline
57
Q

What drug factors should be considered when choosing an antibiotic?

A
  1. In vitro activity and current susceptibilities
  2. Established clinical efficacy
  3. Drug of choice charts
  4. PK and tissue penetration
  5. PD
  6. Side effects
  7. Cost

PT 1 (34 decks)

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