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30 Cards in this Set

  • Front
  • Back
All beta-lactam antibiotics inhibit bacterial growth by interfering with the _______ reaction of bacterial cell wall synthesis
transpeptidation
_______ is probably acylated by penicillin (conformation of penicillin is very similar to that of D-alanyl-alanine)
transpeptidase
homologous recombination between PBP genes of different bacterial species
Acquisition of additional PBP via transposons (methicillin-resistant S. aureus)
acquired resistance
Impaired penetration of drug to target PBP
Occurs only in Gram(-) because of their impermeable outer cell wall membrane
antibiotics cross outer membrane and enter cell via outer membrane protein channels (porins). Down-regulation of porins can impair antibiotic entry (Pseudomonas aeruginosa is resistant to most antibiotics since it lacks porins)
Gram (-) organisms may also produce efflux pumps (transport the antibiotic from the periplasm back across the membrane)
mechanism of penicillin resistance
Class__ (extended spectrum β-lactamase): degrade penicillin, some cephalosporins and some carbapenems
A
Class___(Zn-dependent): destroy all β-lactams except aztreonam
B
Class ___ beta lactamase: cephalosporins
C
Class___ beta lactamase: cloxacillin
D
Class__and __ beta lactamase can be inhibited by clavulanate
A and D
Gram (), β lactamase:
Secreted extracellularly in large amounts
Most are penicillinases
Encoded by plasmids
+
Gram (), β lactamase is located in the periplasmic space, small amounts.
Encoded by plasmids and chromosome
Can hydrolyze both penicillins and cephalosporins
-
works against Gram (+) cocci, sensitive to pencillinase
natural penicillins V and G
Less potent than natural penicillin, used in S. aureus
Penicillinase-resistant penicillins
Methicillin (discontinued), nafcillin, oxacillin, cloxacillin, dicloxacillin
Extended spectrum penicillins that works against Haemophillus influenzae, E. coli, Proteus mirabilis
Aminopencillins
Aminocyllin, amoxycillin
Extended spectrum penicillins that works against Pseudomonas, Enterobacter, Proteus spp.
Carboxypenicillins
Carbenicillin (discontinued), ticarcillin
Extended spectrum penicillins that works against Pseudomonas, Klebsiella
Ureidopencillins
Mezlocillin (discontinued), piperacillin
Low acid stability. Degraded by gastric juices.
Rapidly absorbed orally (max conc. 30-60 min in blood)
Food interference (30 min before meal)
Administered parenterally, in depot release preparations (procaine-penicillin, benzathine penicillin)
penicillin G
(penicillin V is more stable in acid)
Inhibits the growth of penicillinase producing S. aureus
Relatively stable in an acid medium
Absorbed rapidly but incompletely (30-80%)
Eliminated rapidly by kidney. Also hepatic
Isoxazoyl penicillin (oxacillin, cloxacillin, dicloxacillin)
Very effective against S. aureus
Inactivated in the acidic medium
Nafcillin
β-lactamase sensitive
Acid stable
Well-absorbed
Food diminishes absorption
Renal dysfunction prolongs half life
Ampicillin
β-lactamase sensitive
Acid stable
Absorbed quickly; food does not interfere with absorption
Amoxicillin
MOA: inhibition of PBPs
Mechanisms of resistance:
Altered PBP
Beta lactamase (extended spectrum)
Not active against Enterococci and L. monocytogenes
Most are absorbed readily after oral administration
Several can penetrate into CSF
High concentrations achieved in synovial fluid, bile, pericardial fluid
Primarily excreted by kidney
Classified in 4 generations
Cephalosporins
Spectrum: good against Gram (+); modest against Gram (-)
First generation cephalosporins
Antianaerobe activity:
Cefoxitin, Cefmatazole, Cefotetan
Increased activity against Gram (-) but much less active than IIIrd generation
Gram (-) e.g. Klebsiella sp., Haemophilus influenzae
Second generation cephalosporins
Expanded Gram (-) coverage compared to 2nd generation
Some are able to cross BBB
Third generation cephalosporins
Cefepime
Good activity against: P. aeruginosa, Enterobacteriaceae, S. aureus, S. pneumoniae, Haemophilus, Neisseriae
Penetrates in CSF
More resistant to hydrolysis by chromosomal beta-lactamase
Fourth generation cephalosporins
MOA: Binds to PBPs, disrupting cell wall synthesis and is bactericidal.
Broad spectrum (P. aeruginosa sensitive too)
Resistant to most forms of β-lactamase, including that produced by Staphylococcus
Not absorbed orally
Rapidly hydrolyzed by renal dipeptidase, so always administered with cilastatin, an inhibitor of dipeptidase
imipenem
Does not require cilastatin
Similar to imipenem but less likely to cause seizures
meropenem
MOA: Interacts with PBPs
Spectrum: No activity against Gram (+) and anaerobic bacteria are resistant.
Aztreonam is resistant to the β-lactamase produced by Gram (-) organisms.
Side effects: well tolerated. Penicillin allergic patients do not exhibit cross-reactions with aztreonam.
aztreonam
Inhibit β-lactamase (class A and D most sensitive to clavulanic acid)
Poor antimicrobial activity
Included in combination with some beta-lactam antibiotics (amoxicillin)
Clavulanic acid
Sulbactam