Clinical principles of antibacterial usage

Question 1

1. Explain how an antibiogram report may affect empiric antibiotic selection.

Answer 1

Question 2

2. Describe the different methodologies used for antimicrobial susceptibility testing.
3. Define MIC and MBC and their relation in defining bactericidal/bacteriostatic antibiotic activity

Answer 2

Minimum inhibitory concentration (MIC) – the lowest concentration of antibiotic that prevents visible bacterial growth

i. Measured in μg/ml
ii. Measured with E test and broth dilation
iii. MIC for different agents for particular organisms are not directly comparable

Minimal bactericidal concentration (MBC) – lowest concentration of the antibiotic that kills 99.9% of the original inoculum

i. Currently not used to determine susceptibility today
ii. Used to determine bactericidal or bacteriostatic activity
iii. Bactericidal if MBC = MIC
iv. Bacteriostatic if MBC >>>> MIC

Test for beta-lactamase activity

Question 3

2. Describe the different methodologies used for antimicrobial susceptibility testing.

Answer 3

Question 4

4. Interpret the meaning of antibiotic susceptibility categories (e.g., susceptible, intermediate, and resistant)

Answer 4

Susceptible – organism is likely to be inhibited by the normal recommended dosage of an antimicrobial agent

i.Bare minimum for susceptibility is Cp > MIC

Intermediate

Resistant –bacteria tested will not respond to the antibiotic

Caveat for interpretation

i.Not adjusted for site of infection, number of organisms in an infection, conditions in host (ex. pH), or host defenses

Question 5

5. Describe some of the principles involved in determining interpretive breakpoints (i.e. S, I and R).

Question 6

6. Describe how local and host factors contribute to appropriate antibiotic selection.
7. Identify clinical parameters for which bactericidal therapy may be preferred

Answer 6

Question 7

6. Describe how local and host factors contribute to appropriate antibiotic selection.
7. Identify clinical parameters for which bactericidal therapy may be preferred

Answer 7

Host factors

1) Drug allergies
2) Renal/liver function issues
3) Age (sulfonamides in neonates; tetracyclines in kids)
4) Genetic factors
5) Pregnancy
6) Drug interactions: **BOARD worthy material
7) Immune status:

• Neutropenia—bactericidal therapy recommended
• Immunosuppression or neutropenia—type of organisms causing disease may include those not otherwise observed in healthy individuals.