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5224 > Cell Wall Synthesis Inhibitors II > Flashcards

Cell Wall Synthesis Inhibitors II Flashcards

1
Q

When were cephalosporins isolated

A

1948

semi-synthetic abx (synthetic side chain)

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2
Q

What do cephalosporins look like

A
  • all have same cephem nucleus (B-lactam ring fused with dihydrothiazine ring)
    Differ in R1 and R2 side chains
  • R3 = H = cephalosporin
  • R4 = OMe = cephamycins
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3
Q

Characteristics of cephalosporins

A
  • MORE stable than penicillins (less strain on 4 membered ring)
  • good PO drug
  • resistant to many penicillinases/B-lactamases
  • too bulky to fit into active site so can’t be inactivated
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4
Q

MOA cephalosporins

A
  • Identical to penicillin

- Inhibits enzymes so cell wall cannot grow

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5
Q

What is the cephem core

A

B-lactam ring fused to 6-membered ring (called a dihydrothiazine ring)

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6
Q

Mechanisms of resistance to cephalosporins

A

Similar to penicillins

  • inactivation through hydrolysis by B-lactamases (cephalosporinases)
  • Decreases access to the target (decreased entry or active efflux)
  • alteration of the target transpeptidase through mutations
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7
Q

Know these 3 drugs

A

Cephalexin = keflex (PO, 1st generation)
Cefdinir = omnicef (PO, 3rd generation)
Cefuroxime axetil = ceftin (PO, prodrug, 2nd generation)

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8
Q

How are cephalosporins classified

A

by generation based on antimicrobial activity

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9
Q

1st generation cephalosporins

A
  • good against Gram +
  • Modest against Gram -
  • Enterococci, MRSA, and Bacteroides fragilis are resistant
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10
Q

2nd generation cephalosporins

A
  • somewhat better against Gram -
  • active against Bacteroides fragilis
  • more resistance to B-lactamases
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11
Q

3rd generation cephalosporins

A
  • Less active than 1st gen against Gram +
  • more active against Enterobacteriaceae (Gram -), including B-lactamase producers
  • subset active against Pseudomonas aeruginosa (Gram -)
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12
Q

4th generation cephalosporins

A
  • extended spectrum relative to 3rd gen
  • increased stability to plasmid and chromosome-encoded B-lacamases
  • good for empirical tx when Gram +, Enterobacteriaceae, and Pseudomonas possible
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13
Q

PK of cephalosporins

A
  • Cephalexin: PO, Renal excretion
  • Cefuroxime: PO, Prodrug metabolized by hydrolysis, Renal excretion
  • Cefdinir: PO, renal excretion
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14
Q

Which cephalosporin generations have good CSF penetration

A

3rd and 4th; can treat bacterial meningitis

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15
Q

Cefazolin

A
  • 1st generation cephalosporin
  • sometimes preferred over other 1st gen due to long half-life and good tissue penetration (NOT CNS)
  • IM or IV
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16
Q

Cephalexin (Keflex)

A
  • 1st generation cephalosporin
  • UTI and staphylococcal and strep infections
  • Less active against penicillinase-producing staph
  • Can be given orally, so frequently used
  • similar structure to penicillin
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17
Q

Cefuroxime axetil (Ceftin)

A
  • 2nd generation cephalosporin
  • actually a cephamycin (has methoxy group instead of hydrogen)
  • less active against Gram +
  • bulky, so resistant to some B-lactamases
  • PRODRUG of Cefuroxime
  • PO (cefuroxime given IV)
18
Q

Cefaclor

A
  • 2nd generation cephalosporin
  • PO
  • active against haemophilus influenzae and moraxella catarrhalis
19
Q

Cefdinir (Omnicef)

A
  • 3rd generation cephalosporin
  • Active against Gram - and gram +, including those expressing some B-lactamases
  • PO
  • Bulky, so resistant
  • pneumonia, bronchitis, ear infections
20
Q

Cefotaxime

A
  • 3rd generation cephalosporin
  • highly resistant to B-lactamases
  • Good CSF penetration
21
Q

Adverse reactions to cephalosporins

A
  • peptide-like so hypersensitivity –> most common and severe
  • may be cross-reactivity btwn penicillin and cephalosporin hypersensitivity
22
Q

What are carbapenems

A
  • synthetic B-lactam abx
23
Q

What do carbapenems consist of

A
  • B-lactam ring fused to dihydropyrrole ring
  • NO sulfur like in penicillin, replaced by Carbon
  • core is penem (double bond on 5-membered ring)
24
Q

Carbapenems currently used in the US

A
  • imipenem
  • ertapenem
  • meropenem
  • doripenem
  • ALL GIVEN IV
25
Q

What was the first carbapenem

A

Imipenem; developed in 1980’s

26
Q

Imipenem

A
  • WIDE spectrum against: Gram +/-, anaerobes
  • resistant to most B-lactamases, but NOT metallo-B-lactamases
  • renal metabolism via dehydropeptidases
  • administered with cilastatin
27
Q

What is cilastatin

A

dehydropeptidase inhibitor

- prevents metabolism of Imipenem

28
Q

Imipenem MOA

A

same as penicillin and cephalosporin

29
Q

only carbapenem approved for menigitis

A

Meropenem

30
Q

PK of Carbapenems

A
  • penetrate all body tissues well, including CSF
  • excreted renally
  • given IV
  • very stable and avoids most resistance
  • used in complicated cases or intrabdominal infections
31
Q

Adverse effects of carbapenems

A
  • N/V, diarrhea, rashes, and infusion site rxn
  • pt with penicillin allergy may have carbapenem allergy
  • high levels with renal failure and coadministration with foscarnet = seizures
32
Q

Indications for carbapenems

A
  • for infections that are resistant to other abx
  • for mixed aerobic/anaerobic infections
  • Enterobacter infections b/c resistant to Enterobacter B-lactamase
  • infections with Gram - and extended spectrum B-lactamases (ESBL)
33
Q

Resistance to Carbapenems

A
  • Mainly due to hydrolysis by B-lactamases (carbapenemases)
  • specifically Metallo-B-Lactamases and some serine-B-Lactamases
  • carbapenems still rare, so best bet if resistance to other drugs
34
Q

Monocyclic B-Lactams: Monobactams

A
  • sulfonate group attached to N
  • limited to Gram - rods, including pseudomonas
  • side chain identical to R1 of ceftazidime
  • Stable against B-lactamases and metallo-
  • GOOD CSF penetration
  • IV
35
Q

Aztreonam

A
  • only Monobactam available in US
  • IV
  • Good CSF penetration
  • CAN be given to pts with penicillin allgergies
36
Q

Vancomycin

A
  • glycopeptide (mostly peptide with some sugar)
  • Not absorbed well = IV
  • active against Gram +, esp staph (can be given for MRSA)
  • quite stable b/c very bulky
37
Q

Vancomycin MOA

A
  • binds tightly to terminal D-Ala-D-Ala of peptidoglycan, inhibiting cross-linking
  • does not inhibit the transpeptidase enzyme like B-lactams, but inhibits binding to substrate
38
Q

Vancomycin resistance

A
  • due to replacement of terminal D-Ala-D-Ala with D-lactate

- Vanco can’t bind and transpeptidase can cross-link

39
Q

What is Vancomycin used for

A
  • sepsis
  • endocarditis
  • MRSA
40
Q

Vancomycin adverse rxns

A
  • phlebitis at injection site
  • chills and fever
  • “red neck” syndrome due to histamine release

5224 (9 decks)

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