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Disease & Defense > LEC 34 Antimicrobials II > Flashcards

LEC 34 Antimicrobials II Flashcards

1
Q

How do polymyxins (colistin = polymixin E) work?

A
  • destroys the cell membrane
  • most active against Gram-negative bc of the presence of the outer membrane
  • low levels of resistance
  • active against non-growing cells
  • HIGHLY toxic and destroys eukaryotic cell membranes also –> NOT USED OFTEN
  • Generally topical use only; systemic use restricted to tx of serious gram negative infxns
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2
Q

Why has colistin been used more in recent years?

A

d/t the appearance of panresistant bacteria (Pseudomonas, Klebsiella, and Acinetobacter spp)

However, resistance appearing d/t enzyme that modifies lipid A

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3
Q

How does Daptomycin (Cubicin) work?

A
  • Active against GRAM POSITIVE (including MRSA)
  • Exact MOA unknown - binds cytoplasmic membrane resulting in depolarization and disrupts cellular functions (Bactericidal)
  • Not active against gram-negative - can’t pass OM
  • Not active in the lungs - ie not useful for pneumonia
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4
Q

What two classes of drugs are cell wall inhibitors?

A
  • Beta Lactams
  • Glycopeptides
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5
Q

What is the largest class of cell wall inhibiting abx?

A

Beta-lactams

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6
Q

What are the classes of beta-lactams?

A
  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Monobactams
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7
Q

What is the defining structure of a beta-lactam?

A

a four membered ring

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8
Q

How do beta-lactams function?

A
  • target penicillin-binding proteins (PBPs) and inhibit transglycosylation and transpeptidation of cell wall
  • impairs wall remodelling (disrupts cell division)
  • induces autolysins (cell lysis)
  • Bactericidal, but only against growing cells
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9
Q

What structure is characteristic of beta lactams?

A

a 4 membered ring

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10
Q

How is the beta lactam function considered bactericidal?

A
  • Impairs wall remodeling - disrupts cell division
  • Induces autolysins - cell lysis

Bactericidal, but ONLY AGAINST GROWING CELLS

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11
Q

Do beta lactams work on gram negatives?

A

Yes, but it depends on whether it can pass the porins.

Much more effective for gram positive

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12
Q

What is a form of resistance to beta lactams?

A

Production of beta lactamases - degrades 4 membered ring

Generally plasmid encoded

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13
Q

How have drug developers overcome this resistance issue of beta lactamases?

A

They started making beta lactamase inhibitors that are generally given in combo with the beta lactam

Suicide inhibitors of beta lactamases

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14
Q

What are some of the beta-lactam/beta-lactamase inhibitor drugs?

A
  • Ampicillin + sulbactam = Unasyn
  • Amoxicillin + clavulanate = Augmentin
  • Ticarcillin + clavulanate = Timentin
  • Piperacillin + tazobactam = Zosyn
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15
Q

What is Pseudomonas aeruginosa?

A

Gram negative bacillus that has developed pan resistance

other pan resistance: Acinetobacter and Klebsiella

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16
Q

How do you treat Pseudomonas aeruginosa infxn?

A

High dose aminoglycoside (tobramycin) + Extended spectrum penicillin/beta-lactamase inhibitor (ticaricillin-clavulanate or piperacillin-tazobactam)

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17
Q

What do you know about Penicillin G?

A
  • Acid sensitive
  • Poorly absorbed orally
18
Q

What is better about Penicillin V vs G?

A
  • Acid Stable
  • Better absorbed - allows oral dosing
  • Lead to production of better penicillins - amoxicillin & ampicillin
19
Q

Which drug is absorbed better: Amoxicillin or Ampicillin?

A

Amoxicillin (95%)

Ampicillin -> 40%

20
Q

Early penicillins were most effective against what kind of bacteria?

Gram positive or negative?

A

Gram-Positive

Mods were made to increase gram neg coverage and decrease resistance

21
Q

Aminopenicillins (amox & amp) have increased activity against what?

A

Gram-Negatives

22
Q

Carboxypenicillins (carbenicillin & Ticaricillin) and Ureidopenicillins (piperacillin) have what kind of spectrum?

A
  • Increased gram neg spectrum
  • more resistant to beta lactamases
23
Q

What are the semi-synthetic beta lactams and what advantage do they confer?

A
  • Methicillin - acid sens.; not given oral
  • Oxacillin/Nafcillin - acid stable; absorbed from GI tract

Both are beta lactamase resistant

24
Q

How does methicillin resistance occur?

A
  • PBP2A is encoded by the gene mecA on the chromosome
  • PBP2A has a lower affinity for beta lactams
25
Q

First generation cephalosporins (cefazolin, cephalothin) have what kind of spectrum?

A

Narrow spectrum - mostly Gram positive

26
Q

Second generation cephalosporins (cefaclor, cefonicid) have what kind of spectrum?

A

Expanded spectrum - Better Gram negative coverage and some anaerobes

27
Q

Third generation cephalosporins (cefotaxime, ceftriaxone) have what kind of spectrum?

A

Broad spectrum - Even better gram negative coverage, but at the expense of gram positives

28
Q

Fourth generation cephalosporins (cefepime) have what kind of spectrum?

A

Extended spectrum - Broad spec, relatively resistant to beta lactamases

29
Q

What is the 5th generation cephalosporin that binds PBP2A and is therefore active against MRSA?

A

Ceftaroline

formulated as a prodrug

30
Q

What is the spectrum of carbapenems?

A
  • Gram positive cocci but not MRSA or VRE
  • Does however include very problematic gram negs: Klebsiella, Enterobacter, Pseudomonas, Acinetobacter

also includes anaerobe: Bacteroides fragilis

31
Q

How does carbapenem resistance occur?

A
  • Production of carbapenemase (most common)
  • Also inactivated by the human renal enzyme dehydropeptidase
  • Efflux pumps
  • Porin change/loss
32
Q

Which carbapenem is not dehydropeptidase sensitive?

A

Meropenem

33
Q

Imipenem/Cilastatin combo can avoid the dehydropeptidase because why?

A

Cilastatin is a peptidase inhibitor

34
Q

What is the MOA for glycopeptides (vancomycin)?

A

Bind irreversibly to terminal alanines in pentapeptide chain required for cross-linking

Important drugs for Gram +, ESPECIALLY MRSA

35
Q

How does vancomycin resistance occur?

A
  • Intrinsic: can’t pass Gram neg outer membrane
  • Acquired: Substitution of terminal D-alanine with D-lactate

Acquisition of Tn1546

36
Q

What is GISA/VISA?

A
  • Staph aureus with reduced susceptibility but not full blown resistance
  • Thick cell wall - overproduction of terminal alanines so the drug binds at outer surface of cell wall and has trouble penetrating
37
Q

Vancomycin is normally an IV drug, but can be used orally to treat what infection?

A

C. difficle

38
Q

What other two drugs treat C. difficile infections other than vancomycin?

A
  • Metronidazole
  • Fidaxomicin
39
Q

What do you know about Bacitracin?

A

Cell wall inhibitor used topically and often combined with a polymixin to increase the spectrum of activity

40
Q

What do you know about Fosfomycin?

A

Cell wall inhibitor used as a single dose tx for UTIs

41
Q

What do you know about Cycloserine and Isoniazid?

A

Important anti-mycobacterial agents

Disease & Defense (37 decks)

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