Principles of Antibiotic Use

Question 1

susceptibility to drug depends on achieving concentration at _____ that is sufficient to inhibit microbe growth

Answer 1

at the site of infection

Question 2

bacteriostatic vs bactericidal

Answer 2

bacteriostatic: suppress growth, keep bacteria in stationary phase of growth

bactericidal: kill bacteria

Question 3

in general, protein synthesis inhibitors are [bacteriostatic/bactericidal]

while cell wall-active agents are [bacteriostatic/bactericidal]

Answer 3

protein synthesis inhibitors - typically bacteriostatic (except aminoglycosides)

cell wall-active agents are bactericidal, as are rifampin (targets DNA-dependent RNA pol) and quinolones (targets DNA gyrase)

Question 4

MIC vs MBC

Answer 4

MIC (minimum inhibitory concentration): lowest concentration of antimicrobial or drug that will inhibit the visible growth of bacteria

MBC (minimal bactericidal concentration): lowest concentration of antibacterial agent required to kill a particular bacterium

*if MIC is within therapeutic range but MBC is not —> bacteriostatic
*if MBC is within therapeutic range of drug —> bactericidal

Question 5

drug resistance occurs when the concentration of drug….

Answer 5

… required to kill or inhibit microbe is greater than the concentration that can be safely achieved

Question 6

explain how MIC and MBC determine whether a drug is bacteriostatic or bactericidal

Answer 6

*if MIC is within therapeutic range but MBC is not —> bacteriostatic
*if MBC is within therapeutic range of drug —> bactericidal

MIC (minimum inhibitory concentration): lowest concentration of antimicrobial or drug that will inhibit the visible growth of bacteria

MBC (minimal bactericidal concentration): lowest concentration of antibacterial agent required to kill a particular bacterium

Question 7

prophylactic vs empiric vs definitive antimicrobial therapy

Answer 7

prophylactic: prevent colonization or infection by any or all microorganisms - not very effective but appropriate for immunosuppressive patients

empiric: treat all likely pathogens, single broad-spectrum agent preferable but combination therapy also possible (life-threatening situations)

definitive: narrow-spectrum agent specific for identified organism

Question 8

which of these are examples in which prophylactic antibiotic therapy is commonly used?
a. immunosuppressed patients
b. rifampin to prevent meningococcal meningitis in people in close contact to a case
c. prevention of gonorrhea or syphilis
d. TMP-SMX to prevent recurrent UTI by E. coli
e. patients with valves or other structural heart lesions predisposing to endocarditis prior to procedures
f. preventing wound infections after surgical procedures

Answer 8

these are all examples

note that preventing wound infections after surgical procedures is best-studied use

Question 9

Which of these are true regarding combination antibiotic therapy?
a. used for treatment of severe infection when causative organism is unknown
b. used for treatment of polymicrobial infections
c. enhances antimicrobial activity for specific infection
d. has major risk of emergence of resistance
e. reduces toxicity to host

Answer 9

a. used for treatment of severe infection when causative organism is unknown
b. used for treatment of polymicrobial infections
c. enhances antimicrobial activity for specific infection
e. reduces toxicity to host

*actually prevents emergence of resistance (very unlikely a bacteria is resistant to 2+ drugs at once)

Question 10

describe each type of combination antibiotic therapy:
a. synergistic
b. additive
c. indifferent
d. antagonistic

Answer 10

synergistic: one drug affects microbe such that it is more sensitive to inhibitory action of another drug

additive: drugs work independently of one another

indifferent: combination therapy is no different than individual therapy

antagonistic: combination therapy is less effective than individual therapy

Question 11

fill in the blank with either bacteriostatic or bactericidal (can be used multiple times, or not at all:

____ antibiotics frequently antagonize action of _____ antibiotics

____ antibiotics in combination tend to be additive or synergistic

Answer 11

BACTERIOSTATIC antibiotics frequently antagonize action of BACTERICIDAL antibiotics (example: tetracyclines antagonize beta-lactams)

BACTERICIDAL antibiotics in combination tend to be additive or synergistic (example: cell wall synthesis i inhibitors plus aminoglycoside)