Flashcards in Clinical Use of Antibiotics Deck (22):
How can you, as an MD, help with correct diagnosis of microbes?
1. Get sample BEFORE givng antibiotics
2. Tissues, aspirates, fuids>>> "Swabs"
3. More sample > Less
4. Get Deep samples, not superficial (wounds)
T/F Cultures from catheters/drains should ONLY be taken if the catheter/drain is freshly placed.
If its been there for a while, other bacteria are likely to have invaded.
What is Empiric Therapy?
Treatment with antibiotics BEFORE knowing the exact nature of infecting organism.
What are questions to ask yourself when doing empirical therapy?
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,
What are 2 common examples of empiric treatments?
1. Sepsis (life threatening infection)
2. Outpatient treatment of infections (UTI)
How can an Antibiogram help you chose empirical antibiotics?
Anitbiograms are susceptibility charts specific to each hospital, They tell you which bacteria are susceptible to which antibotics for your region.
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?
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?
Can not tell unless samples from the clear tubes are plated. Less than 10 colonies/plate tells you MBC.
What is a Kirby-Bauer (disk diffusion) test?
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.
How does an E-test differ from Kirby-Bauer?
Uses a strip with a concentration gradient of drugs.
Where the bacteria meets the strip, that equals MIC.
Bactericidal antibiotics have which relationship between MBC and MIC?
MBC=MIC for bactericidal antibiotics
Bacteriostatic antibiotics have which relationship between MBC and MIC?
Which is more important for susceptibility testing, MBC or MIC?
What is the difference between a susceptible bacteria and a susceptible-dose dependent?
SDD may be susceptible at certain doses but not others,
What are some problems with the clinical accuracy of susceptibility testing?
Does not account for in vivo circumstances (pH, site of infection, # of organisms, host defense etc)
For a bacterium to be considered susceptible to an antibiotic, what must be true of the antibiotic at normal administered doses?
The antibiotic should have a maximal serum concentration that exceeds the MIC of the bacteria
(in Dr. French’s verbiage, Cp > MIC)
What are some local factors that contribute to antibiotic selection?
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)
What are some infections that require bactericidal drugs?
Host defense cant enter meninges
What are some host factors that must be considered when selecting an antibiotic?
2. Renal/liver Fxn
4. Genetic/metabolic factors (G6PD and sulfonamides=no bueno)
6. Drug-Drug interactions (important for boards)
7. Immune status
What kind of antibacterial would be more likely prescribed to an immunocompromised patient?
Give 2 examples of why age is an important factor when selecting antibiotics.
1. Neonates + Sulonamides= Kernicterus
2. Tetracycline + under 8 yrs= bad teeth