Chemotherapy & Antibiotic Resistance-Kozel Flashcards
Why is it that drug developers have little incentive to develop antibiotics even tho they are very much needed?
b/c you make it & people don’t use.
it is put in reserve for those with antibiotic resistance
while it is in reserve the patent is pending
eventually you lose your rights & you didn’t make that much money while you had them.
How long have antibiotics been around?
millions of years–in organisms that try to resist microbes
T/F It takes between 75-100 years for a patient population to develop antibiotic resistance.
False. Usu like 10-30 years.
What are antibiotics?
Chemical substances produced by various species of microorganisms that are capable of inhibiting, in small amounts, the growth of other microorganisms
What are the guidelines for an ideal antimicrobial?
Selective toxicity bactericidal absence of genetic or phenotypic resistance the proper spectrum non-allergenic minimal side effects active in body water soluble bactericidal levels can be reached in vivo
What is meant by selective toxicity?
kill the bug w/o killing the host
if an antimicrobial isn’t bactericidal & killing bugs–what is it?
bacteriostatic. keeps them from growing
What are the options for a proper spectrum? When do you want each kind?
Broad Spectrum-like if you don’t know which bug you are trying to kill
Narrow Spectrum-for a more focused approach when you have 1 organism in mind.
Why is it important that an anti-microbial be water soluble?
b/c it needs to be able to move around in the body, the blood stream & get to its site of infection.
What are the 5 sites of antibiotic action? Note: these are used as categories of antibiotics.
Cell wall synthesis protein synthesis membrane function or synthesis nucleic acid synthesis metabolic pathways
Why is protein synthesis a good target for antibiotics?
b/c bacteria have different ribosomes than humans. Selective toxicity.
What are the 5 mechanisms of resistance to antibiotics? Note: these are also used to categorize them.
Enzymatic Inactivation Decreased Permeability Efflux Modification of Molecular Target Failure to Convert Inactivate Precursor to Active Form
What is meant by enzymatic inactivation as a means of antibiotic resistance?
microbe makes an enzyme that inactivates an antibiotic. Ex: penicillinase
There is acquired decreased permeability. But the main mechanism of resistance to antibiotics comes from intrinsic decreased permeability. What is this?
Gram negative bacteria are more intrinsically impermeable to antibiotics than gram positive bacteria.
How is efflux a mechanism of antibiotic resistance?
some bacteria actually have pumps that can get rid of antibiotics from the cell
What types of things do bacteria do to modify the susceptible molecular target & resist antibiotics?
Alteration of antibiotic binding site
Protection of target site
Overproduction of target
Binding-up of antibiotic
What are the phases involved in the study of pharmacokinetics of a drug?
Absorption
Distribution
Elimination
What is involved in pharmacodynamics of a drug?
- *relationship b/w drug conc’n & toxic effect to host
* *relationship b/w drug conc’n & antimicrobial effect
What does a good antibiotic need in terms of pharmacokinetics? What is involved in this?
Need to be able to get to the microbe.
Involves:
Absorption from the site of administration
Transfer from plasma to site of infection
Elimination from plasma
Elimination from site of infection
What is MIC?
minimum inhibitory conc’n
the minimum conc’n of antibiotic that will stop bacterial growth
What is MBC? Which types of antibiotics does this apply to?
minimum bactericidal conc’n
minimum conc’n to kill bacteria
this only applies to bactericidal antibiotics–about 50% of all antibiotics
What does it mean to be a bactericidal antibiotic?
kill the microbe!
What are some examples of bactericidal antibiotics?
beta lactams vancomycin fluoroquinolones metronidazole aminoglycosides
What does it mean to be a bacteriostatic antibiotic?
inhibit the organism-don’t kill it
depend on the host’s mechanisms of killing to clear it out.
What are some examples of bacteriostatic antibiotics?
tetracyclines
clindamycin
macrolides
sulfonamides
What is synergy with respect to antibiotics?
this is when a combo of antibiotics produces a larger effect than one alone
in fact-a 2-log10 larger effect!
What is a good example of synergy in antibiotic administration?
penicillin + gentamycin
treatment for: viridans strep meningitis
penicillin facilitates the movement of the gentamycin thru the gram positive organisms.
What is the post antibiotic effect?
Definition: persistent suppression of growth following exposure to an antimicrobial-even when it gets below the MIC
What are the mechanisms of PAE?
slows growth below MIC
alters morphology of the microorganism so that its innate defense mechanisms are altered.
What is Postantibiotic leukocyte enhancement (PALE)?
Increases susceptibility to phagocytosis
Increases susceptibility to phagocytic killing
What are the 3 most used pharmacodynamic outcome parameters?
Time>MIC
AUC/MIC
Cmax/MIC
What’s the deal with the time>MIC outcome parameter?
How long a drug stays above the MIC
Time-dependent killing
Minimal to moderate persistent effects
What’s the deal with the AUC/MIC outcome parameter?
Ratio of the 24-hour serum concentration curve to MIC
Total exposure of microbe to antimicrobial agent
Prolonged persistent effects
What’s the deal with the Cmax/MIC outcome parameter?
Maximum serum concentration/MIC
Concentration-dependent killing
Prolonged persistent effects
What does it mean to be a conc’n-dependent killing agent?
Higher drug concentrations have higher rate and extent of bactericidal activity
What are the main outcome parameters for conc’n dependent killing agents?
Cmax/MIC & AUC/MIC
What are some examples of conc’n dependent killing agents?
aminoglycosides
fluoroquinolones
metronidazole
What does it mean to be a time-dependent (conc’n independent) killing agent?
Bactericidal action is relatively slow
Saturation of killing occurs at low multiples of the MIC
**basically: have slow MOA-want to maximize the time the pt stays just over the MIC. Don’t need a large volume, just long exposure.
What are the main outcome parameters for time dependent (conc’n independent) killing agents?
Time>MIC
What are some examples of time-dependent (conc’n independent) killing agents?
beta lactams
vancomycin
What are bacteriostatic agents? Do they have a post antibiotic effect?
these are antibiotics that only halt the growth of bacteria, don’t kill them.
prolonged PAE
What is the main outcome parameter for bacteriostatic antibiotics?
AUC/MIC
What are some examples of bacteriostatic antibiotics?
tetracyclines
clindamycin
macrolides
sulfonamides
What are antibiotics that are inhibitors of cell wall synthesis?
beta lactam antibiotics
cycloserine
bacitracin
glycopeptide antibiotics-vancomycin
Which antibiotics belong in the category of beta lactam antibiotics? What do they all have in common?
natural penicillin penicillin derivates cephalosporins carbapenems beta lactamase inhibitors **they all possess the 4-membered beta lactam ring
What do beta lactam antibiotics & vancomycin mess with?
peptidoglycan cell wall synthesis
prevent the formation of the transpeptide bridge (glycine bridge)
What are the 2 types of natural penicillins?
Penicillin G (benzyl) Penicillin V (phenoxymethyl)
What is the spectrum of natural penicillins?
narrow spectrum
mostly gram positives-can’t get thru the outer membrane of gram negatives.
What is the structure of natural penicillin?
4 membered beta lactam ring
next to the 5 membered thiazolidine ring
What does a beta lactamase do to penicillin?
it destroys penicillin by cleaving the beta lactam ring
What does amidase do to penicillin?
cleaves the side groups of penicillin
this is actually how you make synthetic derivates
To make synthetic derivates of penicillin you start with what?
Natural Penicillin! G & V
What is the clinical use of natural penicillin?
if a pt isn’t allergic-wide use! cheap & works well
Which of the natural penicillins-G or V-can be taken orally?
Only V can be taken orally.
G is sensitive to gastric acid.
What are penicillin binding proteins? What is their fcn?
these are the target proteins (enzymes) of beta lactam antibiotics
fcn: construction of the pentapeptide-pentaglycine bridges that cross link the peptidoglycan layer
What are some examples of these penicillin binding proteins-the enzymes that make the transpeptide bridge?
Carboxypeptidases
Endopeptidases
Transglycosylases
Transpeptidases
What is the MOA of penicillin?
binds to transpeptide bridge enzymes (penicillin binding proteins)
blocks the cross-linking
bactericidal b/c the cell will eventually lyse from being leaky & having autolytic enzymes
What kind of a bond is there b/w the penicillin binding protein & penicillin?
covalent bond
What are some important mechanisms of resistance to penicillin?
beta lactamase enzyme
prevent access of antibiotic to PBP
alteration of binding site of PBP-reduces the # & affinity of PBP
Where is the genetic info to make a beta lactamase enzyme located?
plasmid
transposable chromosomal gene
How do organisms prevent access of antibiotics to PBP?
- *intrinsic resistance of gram negative bacteria (b/c of their outer membrane)
- *altered porin in N. gonorrhea so that penicillin can’t penetrate
Give some examples of the following type of resistance: Alteration in binding site - reduction in number or affinity of PBP.
- *Newly resistant strains of S. pneumoniae
- *Some forms of penicillin-resistant N. gonorrhoeae
- *Methicillin-resistant S. aureus - MRSA
How can penicillins be manufactured to resist penicillase? What is an example of a drug that has this? What is the tradeoff?
you introduce a bulky group near the site of cleavage
ex: methicillin
tradeoff: 1/10 as potent as natural penicillin
Where does cell wall synthesis occur in gram positive bacteria? What does this mean for penicillin on a mission?
- *occurs at the bottom of the cell wall
- *nearest the membrane, but outside the membrane
- *to get to this site, just have to work thru the bulk of the peptidoglycan
Where does cell wall synthesis occur in gram negative bacteria? What is the significance of this for penicillin on a mission?
- *synthesis occurs in the periplasmic space
* *it has to cross the outer membrane-tough & resistant to hydrophobic drugs.
What alterations do broad spectrum penicillins have to be able to penetrate gram negative bacteria as well as gram +?
they have charged side groups
they are then hydrophilic & can get thru the pore of the outer membrane of gram negative bacteria
What is the drawback to the charged structure of broad spectrum penicillins?
they have the same sensitivity to penicillinase as natural penicillin
Give 2 examples of broad spectrum penicillins with charged side groups.
Ampicillin: + charge
Carbenicillin: - charge
Describe the absorption, fate & excretion of penicillin?
vary in oral absorption rapid renal secretion well distributed to most tissues no penetration to BBB usu time-dependent killing-maximize exposure not conc'n to the drug
Why does penicillin vary in oral absorption?
Some are acid labile-penicillin G & methicillin. These must be injected!
Some are acid stable-penicillin V & semi-synthetic penicillins. These can be taken orally.
How do allergic reactions form to penicillin?
the beta lactam ring can open & bind to host proteins-forming a hapten.
then the body is sensitized to the thiazolidine ring that is waving in the wind.
What are the GI consequences of penicillin?
disturbs normal flora
most prominent with ampicillin
What is the exception to the rule that penicillin doesn’t go thru the BBB?
when there is infection or inflammation in the brain-the BBB becomes more permeable.
So if you have meningitis-you can get that penicillin across!
Is a person who is allergic to penicillin necessarily allergic to cephalosporins?
not necessarily
cephalosporins have the beta lactam ring but they don’t have the thiazolidine ring-instead they have a 6 membered ring.
Are cephalosporins sensitive to beta lactamases?
generally, they are resistant!
Describe the different generations & types of cephalosporins.
1st – Narrow spectrum – Gram positives; some gram negatives
2nd – Expanded spectrum – Gram positives; improved gram negative activity
3rd – Broad spectrum – Gram positives; improved gram negative activity, including Pseudomonas
4th – Extended spectrum – Gram positives; marginally improved gram negative activity
MRSA-active cephalosporins – high affinity for PBP 2a’
Describe the absorption, fate & excretion of cephalosporins.
both oral & injectable forms available for most generations.
some have good CNS penetration
excreted via kidney
What are the risks or drawbacks of cephalosporins?
- *GI: diarrhea, nausea
* *Superinfections possible with broad spectrum cephalosporins
Describe the multifactorial ways in which an organism can develop resistance to broad spectrum cephalosporins.
Altered penicillin binding protein 2 (altered penA gene)
Overexpression of efflux pump (due to mutation in repressor mtrR)
Mutation in porin reduces uptake (penB resistance determinant)
What does the CDC currently recommend for treatment of uncomplicated gonorrhea?
ceftriaxone + azithromycin
Where did antibiotic resistant gonococci emerge?
Southeast Asia
came over after the vietnam war
**now there are cases of resistance in the Western US & even Norway
What are 2 examples of carbapenems? Remember: we are still talking beta lactam antibiotics
imipenem
muropenem
What is the structure of carbapenems?
beta lactam ring
modified alpha ring-eliminates sulfur; still 5 members
How do carbapenems work?
they have a high affinity for PBPs of most gram positives & gram negatives.
What is the spectrum of carbapenems?
broad spectrum
can even penetrate the outer membrane of gram negatives thru a specific OMP
Is carbapenem sensitive to beta lactamase?
highly resistant, actually
b/c of the hydroxyethyl group on C6
Are carbapenems effective against MRSA?
no
So…carbapenems are relatively new. What is their clinical use?
useful for a wide array of infections b/c of the broad spectrum
sometimes used for empirical antibacterial therapy
What’s the deal with carbapenem’s absorption, fate, & excretion?
needs to be injected, b/c poor absorption if taken orally
hydrolyzed by peptidase in renal tubule
What is the solution to the problem of the renal peptidase against carbapenems?
take it with cilastatin!
this is a peptidase inhibitor that blocks the antibiotic’s renal degradation–it’ll last longer
Do carbapenems have a ton of side effects?
not really, pretty well tolerated
can get some allergic reaction via similar mechanism as penicillin
What’s the deal with New Delhi metallo-β-lactamase 1 (NDM-1)?
NDM-1 is encoded by the carbapenem resistance gene blaNDM-1
plasmid that carries it found in common enteric bacilli
resistant to almost all usable antibiotics
blaNDM-1 is carried on a plasmid that carries multiple resistance genes. Which things does it resist?
Imipenems All other beta-lactams Aminoglycosides Tetracyclines Fluoroquinolones
What was the perfect storm in New Delhi that led to this crazy resistant infection via NDM-1?
- *too many antibiotics used in india
- *water treatments that allow some spreading of enterics
- *Note: also seen in elective surgeries in SE Asia