Aminoglycosides Flashcards
how does the in vivo effectiveness of aminoglycosides differ from other Ab such as penicillins and cephalosporins?
aminoglycosides have a concentration-dependent killing action; IOW as the plasma levels increase above the MIC, aminoglycosides kill an increasing proportion of bacteria
briefly describe the time-dependent killing of microorganisms by cephalosporins and penicillins.
the in vivo efficacy is directly related to the time above MIC and becomes independent of concentration once the MIC has been reached
aminoglycosides have killing action that continues even after their plasma levels have declined - what is this effect called?
postantibiotic effect
true or false: aminoglycosides have greater efficacy when administered in multiple smaller doses rather than a single large dose.
false; more effective in a single large dose (this is b/c the time above the threshold of toxicity is much shorter with administration of a single large dose)
true or false: aminoglycosides easily cross the BBB and have a wide tissue penetration
false;
what is the major mode of excretion for amino glycosides? How does this affect choosing pt population?
glomerular filtration - excretion is in direct proportion to creatinine clearance; pts with impaired renal function will not be able to clear the drug as effectively
true or false: in terms of toxicity and aminoglycosides, peak levels are very important.
false: with once-daily dosing, peak levels are less important since they will naturally be very high
true or false: aminoglycosides are bactericidal inhibitors of protein synthesis
true
true or false: aminoglycosides are equally effective against both anaerobes and aerobes
false; they have minimal effectiveness on anaerobes since their penetration through the bacterial cell envelope is partially dependent on an oxygen-dependent active transport
aminoglycosides bind to which ribosomal subunit?
30S
aminoglycosides block protein synthesis in at least 3 ways: 1. block formation of what? 2. cause misreading of what? 3. inhibit what process?
initiation complex; the code on the mRNA template; translocation
which species of bacteria tend to mainly be resistant to aminoglycosides?
streptococci - mainly b/c the drugs cannot penetrate the cell.
describe the method of resistance to aminoglycosides.
group transferases catalyze the acetylation of amine functions - note however that resistance to streptomycin is actually caused by changes in the ribosomal binding site
in most cases, aminoglycosides are used in combination with which other class of Ab? (creating a synergistic effect)
beta-lactams (in fact, when used alone, aminoglycosides are not reliably effective against gram + cocci)
this aminoglycoside plus penicillin is the most effective treatment for enterococcal carditis.
streptomycin
