Antimicrobials 4 Flashcards
MOA of aminoglycosides (there are two)
- irreversibly binds to ribosomenal subunit and causes codon to be misread, they are bactericidal unlike most protein synthesis inhibitors.
- disrupts biofilms (esp gram neg ones)–>displaces calcium and magnesium from the outer cell membrane which disrupts the LPS cross links and destabilizes the outer membrane
why do aminoglycosides have a post antibiotic effect
they irreversibly bind to the ribosomes and kill the bacteria right away
aminoglycosides are really great for what kind of bacteria? How does the drug get into these bacteria?
really great for gram negative bacteria. it gets in via porins in the outer membrane, and are then actively transported through the inner membrane (oxygen dependent, no not effective against anaerobes)
aminoglycosides are not good at disrupting biofilms of gram positive bacteria, UNLESS…
the aminoglycoside is administered with a cell-wall disrupting agent like a beta lactam; they are syngergistic with cell wall disrupting antimicrobials
list some general characteristics of aminoglycosides
- bactericidal
- concentration dependent
- oxygen dependent
- inactivated at low pH
- inactivated by necrotic debris/purulent material–>not good for abscesses
- inactivated by combining with other drugs in syringe
important PK considerations for aminoglycosides?
- not absorbed from GI (topical or injectable)
- not bound to proteins
- does not cross blood brarriers
- eliminated via kidney without prior metabolism
- accumulate in renal cortex ( do not give systemically to food animals)
what are the two big adverse effects of aminoglycosides?
-nephrotoxic: accumulates in renal cortex and damages prox tubule cells
ototoxic: accumulates in inner ear, effets auditory and vestibular, usually ocurs after nephrotoxicity
what are the two aminoglycosides i need to remember?
gentamicin, amikacin
aminoglycosides are important drugs for treating ______ infections, although some newer drugs can treat similar infections with fewer adverse effects (like 3rd gen cephalosporins)
aerobic gram neg
how are gentimycin and amikacin given and what are they commonly used for?
both can be given IV, IM, or SQ
most commonly used to treat joint infections in horses, often combined with local anestheitcs or steroids during routine joint injections as prophylaxsis. can also be used topically for eye and ear infections
how do gentamicin and amikacin differ?
both effective for gram neg, amikacin better for staph, both not good at crossing cell membranes
gentamicin and amikacin can be used topically for ear infections, but are ototoxic…how does this work?
before you put it topically in the ear, you should check to make sure the tympanic membrane is in tact but this isn’t always possible
which is broader spectrum, gentamicin or amikacin?
amikacin (since action against staphs as well as gram neg aerobes)
MOA of macrolides and lincosamides?
prevent polypeptide chain elongation
should you use a macrolide and a lincosamide together?
no! they will interfere with each otherand decrease their efficacy
what are some general characteristics of macrolides and linosamides?
- bacteriostatic
- time dependent
- best against gram +
- often used when penicillin resistance is present
there are 3 macrolides I need to know, what are they?
- erythromycin
- tulathromycin
- tilmicosin
there are 2 lincosamides i need to know, what are they?
lincomycin and clindamycin
tulathromycin and tilmicosin are often used for what?
macrolides used in production animals typically to treat gram negative respiratory pathogens
clindamycin is often used for? lincomycin is often used for?
clindamycin: small animals
lincomycin: swine and poultry
what is the MOST IMPORTANT thing to remember about tilmicosin?
it is cardiotoxic! cattle and sheep tolerate it well but horses, gots, swine, small animals, and HUMANS can die after administration! consider using a safer drug, like tulathromycin instead
lincosamides like lincomycin and clindamycin are contraindicted in
horses, ruminants, rabbits, hamsters, guinea pigs because of adverse effects on GI flora
which has better activity against anaerobes, lincomycin or clindamycin?
clindamycin
clindamycin is most commonly used to treat
pyoderma, dental infections, osteomyelitis
lincomycin most often used to treat
mycoplasma resp infections in pigs
MOA of phenicols
inhibit peptide bond formation –>also inhibits mammalian protein synthesis, particularily mitochondrial protein synthesis in the bone marrow
what are the two chloramphenicols I need to know?
chloramphenicol, florfenicol
what are some general characteristics of chloramphenicol and florfenicol?
- bacteriostatic
- broad spectrum
- time dependent
- distributes to all tissues
what is chloramphenicol used for and what are some adverse effects?
- good for methicillin resistant staph, can also give orally to horses
- causes bone marrow supression in cats
- GI effects: vomiting, diarrhea, anorexia
- may cause fatal aplastic anemia in humans–>where gloves when handling!!
what kind of bacteria is chloramphenicol good for?
basically everything except for pseudomonas
what is the safer version of chloramphenicol? what is it often used for?
florfenicol (does not cause bone marrow suppression) , often used to treat respiratory infections in production animals
florfenicol is not used in horses because
causes colitis and injection site reactions
MOA of fluoroquinolones?
inhibit proper unwinding and replication (inhibits DNA gyrase and some topoisomerase)
general characteristics of fluoroquinolones?
- bactericidal
- concentration dependent
- accumulate intracellularily
what is the only oral antibiotic class good against pseudomonas?
fluoroquinolones
what is the one fluoroquinolone i need to know? what is it commonly used for?
enrofloxacin, used in production animals to treat respiratory disease
which drug should you NOT USE EXTRA LABEL IN PRODUCTION ANIMALS?
enrofloxacin (causes multi drug resistance)
Baytril is the brand name for what drug? what is the class, and what is it used for?
enrofloxacin; fluoroquinolone
used for individual cases of bovine and swine resp disease AFTER first choice has failed, ideally only use with culture and sensitivity results, also used in rabbits and guinea pigs extra-label
