Antimicrobial Review Flashcards
What is the mechanism of action of beta-lactam antibiotics?
cell wall synthesis inhibitors
(by binding to penicillin binding proteins, creating pores in the walls, allowing water to enter the cell, the cell swells and dies)
what are the 2 main subdivisions of beta-lactam antibiotics
- penicillins
- cephalosporins
what are the 4 major subdivisions of penicillins?
- benzylpenicillins
- aminopenicillins
- extended-spectrum (anti-pseudomonal) penicillins
- anti-staphylococcal penicillins
Which of the following is/are NOT covered by benzylpenicillins (penicillin G)? (select all that apply)
A. streptococci
B. staphylococci
C. anaerobes
D. gram negative aerobes
B. staphylococci (because of beta-lactamases)
D. gram negative aerobes
also, they do cover gram + and gram - anaerobes, with the exception of bacteriodes fragilis.
Which of the following is NOT covered by aminopenicillins (amoxicilin, ampicillin)?
A. streptococci
B. staphylococci
C. all anaerobes
D. all gram negative aerobes
B. staphylococci
C. all anaerobes (they do most but higher doses are required AND there is an exception for bacteriodes fragilis)
D. all gram negative aerobes (only some, particularly in urine)
What is the purpose of combining aminopenicillins (amoxicillin, ampicillin) to drugs like clavulanic acid or sulbactam?
these drugs are beta-lactamase inhibitors and this will give broader coverage of streptococci,
some staphylococci (not MRSA), all anaerobes (even bacteriodes), and all gram negative aerobes
T/F: The gram-negative spectrum for cephalosporins INCREASES as the generation # increases.
true
and gram + spectrum decreases.
the anaerobic spectrum is variable.
What are the two 1st generation cephalosporin drugs?
- cefazolin
- cephalexin
which of the following is NOT covered by 1st gen cephalosporins (cefazolin, cephalexin)? (select all that apply)
A. streptococci
B. staphylococci
C. all anaerobes
D. all gram negatives
B. staphylococci (maybe)
C. all anaerobes (esp not clostridium)
D. all gram negatives (cefazolin may get some, but cephalexin no)
what is the 2nd generation cephalosporin that covers staphs and streps (no MRSA), as well as anaerobes, and is typically used for surgical prophylaxis in severe dental disease cases?
cefoxitin
what are the three 3rd generation cephalosporin drugs?
- ceftiofur
- cefpodoxime proxetil
- cefovecin
What is the spectrum of 3rd generation cephalosporins?
streps - yes
staphs - maybe, no MRSA
anaerobes - NOT good for clostridium; cefpodoxime and cefovecin are ok for gram neg
gram negatives - higher doses needed; not great for pseudomonas
T/F: penicillins are better for staphylcocci than cephalosporins
false – opposite
penicillins need a beta-lactamase inhibitor added (ex. amoxi-clav, unasyn)
T/F: beta lactam antibiotics are an excellent choice for streptococci
true
Which 2 divisions of beta-lactam’s have the BEST gram-negative spectrum?
- aminopenicillins (amoxicillin, ampicillin)
and - 3rd generation cephalosporins (cefpodoxime, cefovecin, ceftiofur)
which 2 divisions of beta-lactam antibiotics have the best anaerobic spectrum?
- penicillins
- aminopenicillins
cephalosporins are variable with cefovecin being pretty good.
What is the mechanism of action for aminoglycosides?
inhibit protein synthesis at the 30s ribosomal subunit
T/F: aminoglycosides are inactivated by purulent environments
true
what are 2 drugs within the aminoglycoside class?
- amikacin
- gentamicin
what is the spectrum of aminoglycosides?
- gram negative aerobes
- staphylococci (some MRSs)
NO streps, NO anaerobes
what is the mechanism of action for fluoroquinolones?
DNA gyrase inhibitors (topoisomerase II)
some (pradofloxacin) inhibit topoisomerase IV
what are 5 drugs in the flouroquinolone class?
- enrofloxacin
- marbofloxacin
- orbifloxacin
- pradofloxacin (cats)
- ciprofloxacin (dogs)
Which of the following is/are NOT covered by flouroquinolones? (select all that apply)
A. gram negatives
B. staphylococci
C. streptococci
D. anaerobes
E. rickettsia
F. mycoplasma
C. streptococci (very rarely)
D. anaerobes
T/F: the spectrum of flouroquinolones is similar to aminoglycosides, but flouroquinolones are more active in purulent environments and are safer for the kidneys.
true
but FQs are not safer for the cartilage.
what is the mechanism of action for tetracyclines?
inhibit protein synthesis at the 30s ribosomal subunit
what are 3 drugs in the tetracycline class?
oxytetracycline
doxycycline
minocycline
Which of the following statements is FALSE about tetracyclines?
A. there is lots of resistance from gram positives, gram negatives, and anaerobes
B. tetracyclines are mainly used to treat rickettsia
C. minocycline is better than oxytetracycline
D. the spectrum of tetracyclines is very narrow
D. the spectrum of tetracyclines is very narrow
false – the spectrum is actually broad, there is just a lot of resistance
what is the MOA for potentiated sulfonamides?
folic acid pathway inhibitors
what are 3 drugs in the potentiated sulfonamide class?
- trimethoprim-sulfadiazine
- trimethoprim-sulfamethoxazole
- ormethoprim-sulfamethoxine
T/F: the spectrum of potentiated sulfonamides is broad (gram positives, negatives, and protozoa), but there is a lot of resistance
true – these drugs are known as “jack of all trades, master of none”
in vitro tests are overestimating anaerobic activity, so they are not the best choice for these bacteria. And, they have decreased activity in purulent environments.
what is the MOA of macrolides and lincosamides?
protein synthesis inhibitors at the 50s ribosomal subunit
Which drug class do the following drugs belong to?
erythromycin, clarithromycin, azithromycin
macrolides
what drug class does clindamycin belong to?
lincosamide
note this drug is not to be used in horses or rabbits
which drug classes are BEST for abscesses and intracellular bacteria?
macrolides, lincosamides, and phenicols
what is the spectrum of macrolides and lincosamides?
Gram positive aerobes, as well as anaerobes (clinda and azithro)
what is the mechanism of action for phenicols?
protein synthesis inhibition at the 50s ribosomal subunit
what is the spectrum of drugs such as chloramphenicol and florfenicol?
gram positive aerobes
anaerobes
some gram negatives (though lots of resistance)
mycoplasma
rickettsia
T/F: phenicols are deactivated in purulent environments
false – they are good for abscesses and for intracellular bacteria
what is the MOA of nitroimidazoles?
DNA synthesis inhibition through the production of toxic metabolites
what is the spectrum of metronidazole?
anaerobes and protozoa
it is FDA approved to treat giardia only in dogs.
which 2 classes are protein synthesis inhibitors at the 30s ribosomal subunit?
aminoglycosides
tetracyclines
which 3 drug classes are protein synthesis inhibitors at the 50s ribosomal subunit?
macrolides
lincosamides
phenicols
Which of the following drugs has activity against gram positives? (choose all that apply)
A. beta-lactams
B. tetracyclines
C. poten. sulfonamides
D. 3rd gen cephalosporins
E. macrolides
F. aminopenicillins
G. lincosamides
H. phenicols
I. aminoglycosides (staph)
J. FQs (staph)
A. beta-lactams
B. tetracyclines
C. poten. sulfonamides
E. macrolides
G. lincosamides
H. phenicols
I. aminoglycosides (staph)
J. FQs (staph)
what 6 drug classes has activity against anaerobes?
- penicillins
- tetracyclines
- lincosamides
- phenicols
- nitroimidazoles
- +/- 3rd gen cephalosporins
T/F: benzylpenicillins are NOT absorbed orally
true
potassium penicillin goes IV, procaine penicillin goes IM, and benzathine/procaine penicillin goes IM.
Which penicillins have good oral absorption in dogs and cats?
amoxicillin (best) and ampicillin
Which of the following is NOT true of penicillins?
A. hydrohilic
B. minimal protein binding
C. extensive hepatic metabolism
D. renal elimination (glom filtration and tubular secretion)
C. extensive hepatic metabolism
Which 1st gen cephalosporin drug is well-absorbed orally in dogs and cats?
cephalexin
cefazolin is not absorbed orally.
Which of the following is TRUE of 1st gen cephalosporins?
A. hydrophilic
B. high protein binding
C. extensive hepatic metabolism
D. biliary elimination
A. hydrophilic
they have low-mod protein binding, minimal metabolism, and renal elimination (glom filtration and tubular secretion)
which two 3rd generation cephalosporins are NOT absorbed orally?
ceftiofur (IM/IV) and cefovecin (SQ)
cefpodoxime proxetil is well-absorbed orally in dogs and cats (not horses)
what is the purpose of “proxetil” in cefpodoxime proxetil?
it makes it a prodrug which improves bioavailability
which of the following is FALSE about 3rd generation cephalosporins?
A. lipophilic
B. cefpodoxime has low protein binding
C. ceftiofur has moderate protein binding
D. cefovecin has high protein binding
E. minimal metabolism other than ceftiofur to desfuroylceftiofur
F. renal elimination
A. lipophilic
these drugs are hydrophilic and are confined to the plasma/ECF
T/F: beta-lactam antibiotics are bacteriostatic
false – they are bactericidal
why should you increase dosing frequency for immunocompromised patients receiving beta-lactam antibiotics?
because concentrations should be greater than MIC of the bacteria for 90% of the dosing interval. You do not need to increase the dose, you just need to give the same dose more frequently to extend the time the antibiotic is above the MIC.
T/F: aminoglycosides are NOT absorbed orally
true – they should be given IV or IM
Which of the following is TRUE of aminoglycosides?
A. lipophilic
B. high protein binding
C. extensive metabolism
D. renal elimination
D. renal elimination
they are hydrophilic, minimal protein binding, minimal metabolism, and undergo renal elimination.
Through this renal elimination, they undergo reabsorption from urine into systemic circulation which makes them NOT the safest drugs. This is supportive for the recommendation to place your patient on fluid diuresis to eliminate the drugs faster and reduce toxicity risks.
T/F: aminoglycosides and beta-lactams are concentration-dependent antibiotics
false – Only aminoglycosides are concentration-dependent. This means that maximum concentrations of drug should be 8-10x the MIC of the bacteria. Do not increase dose frequency for these drugs, only increase dose.
Beta-latams are time-dependent.
T/F: ciprofloxacin can only be used in dogs
true
it kills horses
T/F: pradofloxacin absorption is deceased by food so should be given orally prior to a meal
true
T/F: flouroquinolones are NOT absorbed well orally.
false – they have mod-excellent oral absorption.
Enrofloxacin can be given IV/IM/SQ too.
Why are fluoroquinolones good choices for CNS disease, prostate disease, or intracellular organisms?
FQs are lipophilic (enro being the most lipophilic) and therefore they are well-distributed to these sites.
Enrofloxacin gets metabolized into ciprofloxacin, what is this metabolism dependent on?
age and species.
dogs make 40% of cipro, cats make less than dogs, and horses make even less. Young animals barely make any, esp. foals.
T/F: elimination of FQs is mostly renal
true
enro is partially biliary
pradofloxacin is mostly hepatic.
T/F: FQs are bactericidal and time-dependent.
false – they are bactericidal but they are concentration-dependent.
The AUC should be 100-125x the MIC of the bacteria for gram negatives and the AUC should be 50-55x the MIC of the bacteria for gram positives.
This means that you can increase the dose OR increase the frequency, but do NOT take a daily dose and split it into half twice daily because this decreases efficacy.
