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ANTIBIOTICS-1 (only exam 1 material)
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Antibiotics produce what 2 effects?
1- bacteriostatic
2- bacteriocidal
Antibiotics selectively inhibit the growth or survival of microorganisms at _____ concentrations.
low
What is the purpose of the
MIC (minimum inhibitory concentration)
value?
It is the
lowest concentration
where an antibiotic will
produce a static or cidal effect
What is the
clinical dose
of an antibiotic?
It must have a plasma concentration of
~4-8 times the MIC value
with
minimum to no toxicity to the patient
What is a bacterio
static
antibiotic?
It
stops
the bacteria from dividing
What is a bacterio
cidal
antibiotic?
It
kills
the bacteria
What 2 classes of antibiotics have a
bacteriostatic
effects?
Tetracyclines
Sulfonamides
What 4 classes of antibiotics have bacteriocidal effects?
Penicillins
Aminoglycosides
Polypeptides
Quinolones
True or false, you can predict whether or not an antibiotic is cidal or static based on the MOA.
True
False
False!
True or false, if a patient is
immunocompromised
they can take a
static
antibiotic.
True
False
False, only immunocompetent patients can be prescribed static antibiotics
Can all antibiotics exhibit a
cidal
effect?
Yes if given at
high concentrations
Can all antibiotics exhibit
both static and cidal effects
?
Yes, the majority of antibiotics have 2 doses (static and cidal)
What 4 factors determine the effect (static or cidal) of an antibiotic?
1- concentration
2- MOA
3- microbial susceptibility/resistance
4- microbial species
Can an antibiotic exhibit
only a cidal effect
regardless of concentration?
Yes only 2 classes:
1- beta-lactams
2- polypeptides
Can an antibiotic
known to be cidal
suddenly
become static
?
Yes because of microbial resistance
What is the purpose of using a
narrow-spectrum antibiotic
?
It
minimizes
microbial resistance
It is
cheaper
to use
What is a broad-spectrum antibiotic?
An antibiotic that is
effective
against a
large number of bacterial strains
and gram positive and negative bacteria
What are the
3 advantages
of using combination therapy?
1- provide
emiric(inital)
therapy
2- treat
polymicrobial(mixed) infections
3- obtain enhanced antimicrobial activity (
synergism
)
What are the
4 disadvantages
of using combination antimicrobial therapy?
1- increased toxcicity
2- increased cost
3- antagonism
4- microbial resistance
What is synergisim?
A
four-fold or greater reduction
in the MIC or MBC of each drug when used in combination vs. when used alone
What is
antagonism
in combination therapy?
When the
combined effect of the drugs are less when used together
vs. when they are used alone
What is
indifference
in combination therapy?
When the
combined effect of the drugs is the same
vs. when used alone
What is the purpose of the
FIC (fractional inhibitory concentration) index
?
It illustrates the interaction between 2 antimicrobial agents
What is the
FBC (fractional bactericidal concentration) index
?
When you
substitute the MBC (min bactericidal concentration) for the MIC
in the FIC Index equation
Synergisim
for combinations of 2 drugs requires an FIC or FBC index of _______
0.5 or less
Antagonism
for combination of 2 drugs requires an FIC or FBC index of ________
4 or more
Indifference
for combinations of 2 drugs requires and FIC or FBC index of ______
0.5 to 4
What are the
4 mechanisms of synergistic action
?
1-
blockade of sequential steps
in a metabolic sequence
2-
inhibition of enzymatic activation
3-
enhancement of antimicrobial agent uptake
by bacterial cells
4-
binding enhancement
What are the
2 mechanisms of antagonistic action
?
1-
inhibition of cidal activity by static agents
2- induction of
enzymatic activation
Microbes can aquire genes (including those for resistance) via _______ ________ from members from their own species or from an unrelated species.
direct transfer
What are the
4 mechansims for microbial resistance
to antimicrobial therapy?
1- drug inactivation via enzymes
2- target modification
3- alteration of target accessibility
4- development of altered metabolic pathways
What is target modification?
Changing the chemistry of a binding site on a microbe so that the antibiotic cannot bind
What are the
2 types genetic origin (r-factors)
in microbial reisistance?
1- chromosomal
2- extrachromosomal
What are the
2 origins
of microbial resistance?
1- non-genetic
2- genetic
True or false, chromosomal resistance contributes the most to microbial resistance?
True
False
False,
extra-chromosomal
resistance contributes the most because the plasmid can be easily transferred
What causes
chromosomal
resisitance?
A spontaneous mutation
What causes extrachromosomal resisitance?
The transfer of R-factors (plasmids)
Chromosomal mutations lead mainly to _____ _______ as the reisitance mechanism.
target modification
Transfer of R-factors leads mainly to _______________ as the resistance mechanism.
drug inactivation by enzmyes
What are the 4 mechanisms to transfer R-factors?
1- transformation
2- transduction
3- conjugation
4- transportation
What is
transformation
?
Does it contribute to the spread of resistance?
Direct insertion of an R-factor into a bacterial cell
It does NOT contribute to the spread of resistance
What is
transduction
?
When R-factors are transferred from 1 bacteria cell to another via a virus
What is
conjugation
?
When R-factors are transferred via mating
What is the
most important mechanism
for transferring R-factors?
Conjugation
What is
transposition
?
Transfer of R-factors via transposons (jumping genes)
*Leads to chromosomal resistance
Author
dr.fizzle
ID
64502
Card Set
ANTIBIOTICS-1 (only exam 1 material)
Description
725
Updated
2011-02-07T00:14:14Z
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