Beta Lactams and Aminoglycosides Flashcards
what is the mechanism of action for penicillins
inhibition of cell wall synthesis
what are three main adverse effects of penicillins
1) hypersensitivity (incl. contact hypersensitivity, not used topically)
2) potentially fatal colitis in hindgut fermenters with oral administration
3) reduction of seizure threshold (Beta lactams inhibit GABAa receptors in the brain)
what spectrum does penicillin G cover
Gram +ve aerobes, anaerobes
what spectrum does amoxicillin cover
Gram +ve aerobes, anaerobes, several Gram -ve aerobes
what pencillin drugs are first line vs second line
first line = penicillin G, amoxicillin
second line = potentiated penicillins
what are the PK features of penicillin (3)
-excreted intact in the urine
-penicillin G is not acid stable
-oral bioavailability of amoxicillin is 90%
mechanism of action of cephalosporins
inhibition of cell wall synthesis
main adverse effects of cephalosporins (3)
-hypersensitivity
-oral administration may cause potentially fatal colitis in hindgut fermenters
-reduction in seizure threshold
what spectrum does first generation cephalosporins cover
gram +ve aeroves, anaerobes, some gram -ve aerobes
what spectrum does third generation cephalosporins cover
mainly gram -ve aerobes
what cephalosporins drugs are first line vs second line
first line = first generation
second line = third generation
PK features of cephalosporins (3)
-only a few are acid stable (eg cephalexin)
-not destroyed by penicillinases, but may be inactivated by some beta lactamases
-some third generation drugs enter CNS readily
mechanism of action for aminoglycosides
inhibition of protein synthesis (bactericidal effect)
main adverse effects of aminoglycosides (2)
-nephrotoxicity
-ototoxicity
general spectrum of aminoglycosides
gram -ve aerobes, staph, mycoplasma
first line vs second line for aminoglycosides
first = topical administration
second = systemic administration
PK features of aminoglycosides (2)
-highly ionized (negligable oral or topical administration)
-food residues > 1 year with parenteral administration
what is the most commonly used AMD?
penicillins
what can destroy the BL ring in penicillins?
warming or freezing temperatures
how is pencillin half life increased?
depot formulations…. pencillin bound to procaine or benzathine, where penicillin slowly dissociates from it at the IM/SQ injection site
penicillins are only effective against _____ bacteria
growing
why do pencillins work best on gram positive bacteria
because they have a thick unprotected peptidoglycan layer
what bacteria is resistant to penicillin drugs
-poor penetration of outer lipid bilayer in gram negative bacteria
-acquired bacterial penicillinases (plasmid encoded, can be transfered from other bacteria)
is penicillin narrow or broad spectrum?
narrow
what is an example of an extended spectrum pencillin?
amoxicillin
what does amoxicillin cover
gram positive aerobes, anaerobes, and SOME gram negative aerobes (many enterobacteriaceae)
how can bacterial penicillinases be inactivated ? example of a drug
with penicillinase inhibitors such as clavulanic acid
clavamox! amoxicillin+clavulanic acid formulation
how to tell if a drug is a cephalosporin name wise
starts with ceph or cef
what are third generation cephalosporins mainly effective against
gram negative aerobes
how well do third generation cephalosporins enter the CNS
reasonably well
are cephalosporins effective if administered orally
no…. most are not acid stable
what is an example of a first generation cephalosporin? route of administration?
cephalexin, oral
what do first generation cephalosporins cover
gram +ve aerobes, anaerobes, some gram -ve aerobes
what are example of first generation cephalosporins that are administered parenternally
-cefazolin; used for surgical prophylaxis in small animals (injectable)
-cephapirin; intramammary for cattle
what are third generation cephalosporins mainly used against? what can they cover in addition to that?
mainly covers gram -ve aerobes
covers some gram +ve aerobes, some anaerobes
example of a third generation cephalosporin and what its used for
ceftiofur; resp infections in livestock, metritis and foot rot in cattle, UTI in dogs
example of a third generation cephalosporin in small animals and duration
cefovecin/convenia; used for resp and skin infections in dogs/cats
2 week formulation essentially guarantees inappropriate duration of therapy in many patients
two main clinical uses of aminoglycosides
1- systemic administration for dangerous gram -ve aerobic infections (septicemia)
2- topical (staph)
do aminoglycosides cross membranes well
no, they are highly ionized which causes limited ability to cross membranes
what route of administration is needed for systemic treatment with aminoglycosides
parenternally
do aminoglycosides kill bacteria
yes!
what is resistant to aminoglycosides
-anaerobes…. because entry of drug into the cell requires oxygen dependent transporter that is absent in anaerobes
-plasma acquired aminoglycosidase
what antibiotic should you never give a dehydrated patient or renal disease patient? why?
aminoglycosides! ordinary dose can be very damaging to kidneys of these patients
how do you minimize damage to kidneys when giving aminoglycosides
by allowing a washout period… give single daily dose and allow concentrations to fall for remainder to the day
can you use aminoglycosides in food animals
-you can…. but IM use in cattle may result in drug residues detectable for more than a year
what do you need to ensure before using topical otic aminoglycoside
ensure tympanum is intact… otherwise can cause permanent hearing loss
what is the most commonly used AG? spectrum?
gentamicin
broad spectrum
when is tobramycin used
used second line for infections resistant to gentamicin
when is amikacin used
used second line for infections resistant to gentamicin
resistant to many aminoglycosides
