B3.022 Las Drogas Flashcards
how do inhibitors of cell wall synthesis work?
B-lactams and vancomycin block enzymatic steps outside of the cell or in the periplasmic space
other ICWS act at intracellular sites
general workings of penicillin
very selective toxicity (high chemotherapeutic index)
bactericidal in growing, proliferating cells
primarily used for gram +
mechanism of action of penicillin
- covalent binding to transpeptidases/penicillin binding proteins
- inhibition of transpeptidase reaction (cross linking of cell wall)
- activation of murein hydrolases (autolysins)
penicillin absorption
oral
acid-sensitive
can also be parenteral (IV, IM)
penicillin distribution
good to most tissues and fluids
poor penetration into eye, prostate and CNS
penicillin metabolism
variable
not usually significant
penicillin excretion
excretes by tubular secretion (organic acid secretory system)
EXCEPTION: nafcillin in bile
oxa-,cloxa- in urine and bile
short half life
which drugs exhibit time dependent killing
pens
cephs
vancomycin
time above MBC relates to efficacy
pen G
pen V
primarily useful against gram +
anti staph penicllins
nafcillin methicillin oxacillin cloxacillin B lactamase resistant
extended spectrum penicillins
ampicillin amoxicillin ticarcillin piperacillin mezlocillin extended gram - activity
anti-psuedomonal penicilins
ticarcillin
piperacillin
mezlocillin
effective against proteus, pseudomonas
problem w anti-pseudomonal penicillins
rapid emergence of resistance
use in combo w aminoglycosides or fluoroquinolones
POWERFUL: use only when indicated, protect therapeutic value
ampicillin rash
10% incidence
90% for mononucleosis patients
self limiting, often does not recur
hypersensitivity reaction of penicillins
major adverse effect 10-15% claim allergy complete cross reactivity not dependent on dose rapid onset
other adverse effects of penicillins
seizures induced by high doses
particularly in renal failure
3 primary resistance mechanisms to penicillin
- no cell wall, no activation of murein hydrolases, metabolically inactive
- inaccessible PBPs
- gram neg
- MRSA - B lactamase production
- plasmid mediated
- either use B lactamase resistance pens or co administer B lactamase inhibitor
problems associated with penicillin use/overuse
sensitization
selection for resistant strains
superinfections by resistant organisms
general overview of cephalosporins in comparison to penicillin
structure and function similar to penicillins
less sensitive to B lactamases
broader spectrum of activity
some cross reactivity w pen-sensitive patients
more expensive than pens
absorption of cephs
poor oral
toxicity of cephs
more toxic than pens
particularly renal
should you use a pen or ceph?
if a pen will work, use it
cephs secondary ICWS
describe the ceph classification system
1, 2, 3, 4 generation chronology of development and use as they progress you get: -greater gram - activity -some with less gram + activity (2) -less B lactamase sensitivity -cephalosporinase resistant (4) -less toxic -better distribution (especially to CNS)
first gen ceph
cefazolin
cephalexin
narrow spectrum
chemoprophylaxis
second gen ceph
cefuroxime
cefotetan
cefaclor
intermediate spectrum
third gen cep
cefotaxime ceftriaxone ceftazidime cefpodoxime broad spectrum
fourth gen ceph
cefepime
broad spectrum
adverse effects of cephs
local irritation from injection
renal toxicity–tubular necrosis, interstitial nephritis; may be enhanced by aminoglycosides
hypersensitivity - 1% cross reactivity with penicillins, more common in early generation
disulfram effect
cefotetan
cefoperazone
bleeding and platelet disorder (give vitamin K)
other B lactams
monobactams - aztreonam carbapenems - imipenem meropenem B lactamase inhibitors: -clavulanic acid -sulbactam -tazobactam
azetreonam
monobactam
gram - activity (doesn’t work against gram + or anaerobes)
B lactamase resistant
crosses blood brain barrier
no cross reactivity in penicillin-sensitive patients
imipenem
carbapenems broad spectrum (gram +, Gram -, and anaerobes) B lactamase resistant IV only crosses blood-brain barrier
discuss the resistance mechanisms to imipenem
pseudomonas develops resistance rapidly, use with aminoglycosides
inactivated by renal dipeptidase in host (co administer Cilastatin)
meropenem
dipeptidase-resistant carbapenem
vancomycin mechanism
inhibits transglycosylation (step before transpeptidation) bactericidal for gram +
vancomycin administration
IV for systemic use
oral for C.diff
vancomycin uses
MRSA
synergistic w aminoglycosides
vancomycin dependent enterococci
vancomycin excretion
IV drug cleared through kidney
vancomycin adverse effects
enhances oto- and renal toxicity of aminoglycosides
red neck syndrome - histamine release
misuse/overuse issues
fosfomycin
newest ICWS
gram + and gram -
fosfomycin mechanism
inhibits cytoplasmic step in cell wall precursor synthesis
active uptake by G6P transporter
fosfomycin administration
oral and parenteral
oral only in US
single dose therapy for UTI
fosfomycin metabolism and excretion
excreted by kidney
synergistic w B-lactams, aminoglycosides, or fluororquinolones
bacitracin
markedly nephrotoxic
topical ONLY
OTC
B lactamase inhibitors:
- clavulanic acid
- sulbactam
- tazobactam
membrane active drugs
polymixin B
polymixin E
polymixin mechanism
basic peptides, act as detergents
polymixin uses
gram - EXCEPT proteus and Neisseria
limited to topical use due to systemic toxicity (renal)
salvage therapy for highly resistant Acinetobacter, Pseudomonas, and Enterobacterieae
give an overview of the inhibitors of protein synthesis (IPS) drug class as a whole
target is “different” in pathogen than host due to differing ribosome sizes
different sites for different drugs (30S vs 50S)
different steps in protein synthesis blocked by different drugs
most reversible and bacteriostatic (except aminoglycosides)
less selective toxicity than ICWS
tetracyclines mechanism
reversible binding to 30S subunit
bacteriostatic
selectivity based on bacterial uptake
tetracyclines pharmacokinetics
urually oral, but absorption variable
chelate metal ions
not absorbed (do not administer w food)
rarely given IV
tetracyclines distribution
well distributed, except to CNS and synovial fluid
concentrates in teeth, bone, liver, kidney
cross the placenta and are excreted in milk
tetracyclines excretion
doxycycline mostly fecal
others mostly urine
clinical uses of tetracyclines
first broad spectrum antibiotic
gram + and gram -
mycoplasma, chlamydia, rickettsiae
Lyme disease
tetracycline adverse effects
GI irritation
superinfections
impaired liver function (high doses, during pregnancy, pre existing liver disease)
photosensitization
calcium chelation (discoloration, growth retardation, deformity)
resistance to tetracyclines
decreased uptake, efflux pumps are major mediators
altered ribosomal proteins or RNA are secondary mechanisms (pseudomonas, proteus)
indiscriminate use/overuse has fostered emergence of resistance
new tetracyclines
glycylcyclines (tigecycline)
retain antibacterial spectrum but overcome resistance
not affected by efflux pump
black box warning due to increased risk of death
other tetracyclines
tetracycline
doxycycline
minocycline
macrolide antibiotics
erythromycin
clarithromycin
azithromycin
bacteriostatic or cidal depending on dose
macrolide pharmacokinetics
absorbed from GI tract, but acid labile use enteric coating or erythromycin esters also administered IV excellent distribution except to CNS crosses placenta excreted in bile half life 1-5 hours EXCEPT azithromycin
clinical uses of macrolides
gram + bacteria, same gram - some mycobacteria
backup for penicillins in pen–sensitive patients
azithro and clarithro are broader spectrum
mycoplasma pneumonia, Legionnaires, chlamydia