Clinical Use of Antibiotics

Question 1

How can you, as an MD, help with correct diagnosis of microbes?

Answer 1

1. Get sample BEFORE givng antibiotics
2. Tissues, aspirates, fuids»> “Swabs”
3. More sample > Less
4. Get Deep samples, not superficial (wounds)

Question 2

T/F Cultures from catheters/drains should ONLY be taken if the catheter/drain is freshly placed.

Answer 2

True

If its been there for a while, other bacteria are likely to have invaded.

Question 3

What is Empiric Therapy?

Answer 3

Treatment with antibiotics BEFORE knowing the exact nature of infecting organism.

Question 4

What are questions to ask yourself when doing empirical therapy?

Answer 4

1. What is the infectious syndrome?
2. What are the common pathogens for this syndrome?
3. What is the likely antibiotic resistance?
4. Whats the most appropriate antibiotic to use?

This is mostly FYI I think,

Question 5

What are 2 common examples of empiric treatments?

Answer 5

1. Sepsis (life threatening infection)

2. Outpatient treatment of infections (UTI)

Question 6

How can an Antibiogram help you chose empirical antibiotics?

Answer 6

Anitbiograms are susceptibility charts specific to each hospital, They tell you which bacteria are susceptible to which antibotics for your region.

Question 7

A bacteria is cultured in a broth dilution with antibiotics. The concentrations of drugs in the tubes are 1, 2, 4, 8, 16, 32, 64. The tubes from 1-8 are cloudy, 16-64 are clear. What is the MIC?

Answer 7

16

Question 8

A bacteria is cultured in a broth dilution with antibiotics. The concentrations of drugs in the tubes are 1, 2, 4, 8, 16, 32, 64. The tubes from 1-8 are cloudy, 16-64 are clear. What is the MBC?

Answer 8

Can not tell unless samples from the clear tubes are plated. Less than 10 colonies/plate tells you MBC.

Question 9

What is a Kirby-Bauer (disk diffusion) test?

Answer 9

Kirby Bauer

1. Culture bacteria on large agar plate with antibiotic disks with varying drugs and concentrations
2. Measure diameter around disks after incubation to determine best susceptibility.

Question 10

How does an E-test differ from Kirby-Bauer?

Answer 10

Uses a strip with a concentration gradient of drugs.

Where the bacteria meets the strip, that equals MIC.

Question 11

Bactericidal antibiotics have which relationship between MBC and MIC?

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Answer 11

MBC=MIC for bactericidal antibiotics

Question 12

Bacteriostatic antibiotics have which relationship between MBC and MIC?

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Answer 12

MBC»>MIC

Question 13

Which is more important for susceptibility testing, MBC or MIC?

Answer 13

MIC

Question 14

What is the difference between a susceptible bacteria and a susceptible-dose dependent?

Answer 14

SDD may be susceptible at certain doses but not others,

Question 15

What are some problems with the clinical accuracy of susceptibility testing?

Answer 15

Does not account for in vivo circumstances (pH, site of infection, # of organisms, host defense etc)

Question 16

For a bacterium to be considered susceptible to an antibiotic, what must be true of the antibiotic at normal administered doses?

Answer 16

The antibiotic should have a maximal serum concentration that exceeds the MIC of the bacteria
(in Dr. French’s verbiage, Cp > MIC)

Question 17

What are some local factors that contribute to antibiotic selection?

Answer 17

1. Drug distribution (plasma vs tissue)
2. Protected local environments (stuff like blood brain barrier)
3. Bladder action (concentration in urine)
4. Oddities (Daptomycin kills S. pneumoniae, but is inactivated in lung)

Question 18

What are some infections that require bactericidal drugs?

Answer 18

1. Meningitis
2. Endocarditis

Host defense cant enter meninges

Question 19

What are some host factors that must be considered when selecting an antibiotic?

Answer 19

1. Allergy
2. Renal/liver Fxn
3. Age
4. Genetic/metabolic factors (G6PD and sulfonamides=no bueno)
5. Pregnancy
6. Drug-Drug interactions (important for boards)
7. Immune status

Question 20

What kind of antibacterial would be more likely prescribed to an immunocompromised patient?

Answer 20

Bactericidal.

Question 21

Give 2 examples of why age is an important factor when selecting antibiotics.

Answer 21

1. Neonates + Sulonamides= Kernicterus

2. Tetracycline + under 8 yrs= bad teeth

Question 22

What are 2 clinical parameters that would have you leaning towards bactericidal therapy?

Answer 22

1. Immunocompromised individuals

2. Isolated infections away from host defense. (Meningitis, endocarditis, joint infections)