Therapy for Staph and Strep I Flashcards
Concentration dependent
Increase the rate of bacterial killing as the antibiotic concentration increases.
Concentration dependent drug examples
Lipopeptides (daptomycin), aminoglycosides, fluoroquinolones
Time dependent
Killing is predicted by the time that the concentration is above a certain level called the MIC (minimum inhibitory concentration)
Time dependent drug examples
Beta-lactams, glycopeptides (vancomycin)
MIC
Minimum inhibitory concentration, the lowest concentration of an antibiotic that will inhibit the visible growth of bacteria in vitro.
Broth Macrodilution
Put different concentrations of antibiotic into test tubes with bacteria. See which one is the first without cloudiness.
E Test
Uses a strip with varying doses of antibiotic. Place on a dish, read the zone of inhibition.
Bacteriostatic drugs and example
Arrest bacterial growth (linezolid)
Bactericidal drugs and example
Kills bacteria (beta lactams, etc).
Is vancomycin bacteriostatic or bactericidal?
It depends on the organism!
Beta Lactam Antibiotics
Penicillins: Amoxicillin, Ampicillin, Nafcillin, Penicillin
Cefalosporins: Cefazolin (first generation)
How do beta lactams work?
Bind to PBPs and inhibit transpeptidases.
What is the best orally absorbed penicillin?
Amoxicillin
How are penicillins eliminated?
Renally, with the exception of nafcillin.
Natural penicillin is drug of choice for…
S. pyogenes, S. galactiae, treponema pallidum (syphilis).
Penicillin G vs Penicillin V
Penicillin G is IV preparation whereas penicillin V is acid stable and can be taken orally.
Problem with natural penicillin?
Susceptible to penicillinases especially in Staph aureus.
Anti-staphylococcal penicillin
Nafcillin (IV), resistant to penicillinase. No gram-negative activity.
Does nafcillin work on gram negative organisms?
No.
What organisms does natural penicillin work on?
Gram positive cocci, gram negative cocci, gram positive bacilli, spirochetes.
Extended Spectrum Penicillins (amino-penicillins)
Ampicillin and amoxicillin (both oral).
What are amino-penicillins the drug of choice for?
Listeria monocytogenes
What organisms do amino-penicillins work on?
Gram positive organisms, some gram negative activity, some anaerobic activity, ENTEROCOCCI.
What must organisms have to be affected by beta lactams?
Peptidoglycan wall (mycoplasma is inherently resistant)
How is MRSA so drug resistant?
It has an altered PBP that has lower affinity for all beta lactams except ceftaroline.
Betalactamase inhibitors
Clavulanic acid, Sulbactam, tazobactam. Abundant in STAPH AUREUS
Betalactamase inhibitors combined with beta lactams
Clavulonic acid and amoxicillin = augmentin
Sulbactam and ampicillin
These have increased gram negative activity.
Penicillin hypersensitivity
Penicilloic acid can cause IgE mediated hypersensitivity
Penicillin rash common in patients with…
EBV
Penicillin diarrhea caused by
alterations in the commensal flora of the GI tract. C diff can overgrow
Why isn’t methicillin used clinically?
Because it can cause nephritis
Cephalosporins
5 generations. Higher generations have increased gram negativity and higher Vd.
Cefazolin used for
Gram positive cocci like staph aureus, strep (GAS, GBS, viridans), also some activity against gram negative bacilli (e.coli)
What can’t cephalosporins treat?
Enterococci or listeria
Is cefazolin penicillinase resistant?
Yes!
Adverse reactions of cephalosporins
Hypersensitivity
