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Microbiology & Infectious Diseases > 17: Pharmacology - Beta-lactams & Vancomycin > Flashcards

17: Pharmacology - Beta-lactams & Vancomycin Flashcards

1
Q

Name the four broad categories of beta-lactam antibiotics.

A
  1. Penicillins
  2. Cephalosporins
  3. Monobactams
  4. Carbepenams

NB: Beta-lactamase inhibitors co-form’d w/ other beta-lactam abx

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2
Q

How do beta-lactam antibiotics work?

A

Antibiotics have beta-lactam nucleus which inhibits penicillin binding proteins (PBPs) and are bactericidal.

Inhibit the enzymes transpeptidase (L-lys to D-ala) & carboxypeptidase (release ATP) that cross-link NAM-NAG+oligopeptides (cell-wall peptidoglycans).

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3
Q

Describe three mechanisms of bacterial resistance against beta-lactam antibiotics.

A
  1. Alter bacterial cell wall permeability
  2. Alter affinity of PBPs to beta-lactam
  3. Break down beta-lactams (via beta-lactamases)
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4
Q

Name the types of beta-lactamases.

A
  1. Penicillinases
  2. Cephalosporinases
  3. Extended-spectrum beta-lactamases (ESBLs): confer resistance against 3rd generation cephalosporins
  4. ampC beta-lactamases (ampCs): confer resistance against 3rd generation cephalosporins
  5. Carbapenamases: serious problem in NYC ICUs (few effective abx against)
  6. Metallo-beta-lactamases (e.g., NDM-1): resistant against almost all abx
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5
Q

In S. aureus, which gene confers resistance to anti-staphylococcal penicillins, and how? (MRSA)

A

PBP-2a.

Decreases affinity for beta-lactam abx.

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6
Q

Name three drugs can be used to treat MRSA.

A

Linezolid

Vancomycin

Daptomycin

(“Let’s vanquish diseases.”)

NB: Vancomycin preferred.

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7
Q

What antibiotic resistance mechanism can Streptococcus pneumoniae acquire?

A

Alterations in its PBPs resulting in relative or absolute resistance to penicillins (in rare cases, cephalosporins).

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8
Q

What is the pharmacology of beta-lactam antiboitics?

A
  • Time-dependent: work better as long as concentration is above MIC; does not matter how much higher above.
  • Half-life: relatively short; must dose every 4-6 hours.
  • Volume of distribution: excellent penetration into bodily fluids (not so much CSF, unles if meningeal inflammation).
  • Metabolism: low.
  • Clearance: Mostly via kidney (renal), except for oxacillin; must adjust dose for patients w/ renal impairment.
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9
Q

What are some of the adverse effects associated with beta-lactam antiboitics?

A
  • CNS:
    • Encephalopathy
    • Seizures (particularly due to carbapenams at high dose in patients with renal insufficiency)
  • GI:
    • All abx may cause GI upset
    • Diarrhea
    • Wiping out normal gut flora predisposes patients to C. dificile colitis
    • Ceftriaxone causes biliary sludge (esp. in infants)
  • Renal:
    • Interstitial nephritis (particularly oxacillin)
  • Immune-mediated
    • Various cytopenias (neutropenia most common)
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10
Q

Describe allergies to beta-lactam antibiotics.

A
  • Immediate vs. delayed
    • Type I vs. Type II-IV hypersensitivity
  • 5-10% of patients have penicillin allergy, but most can tolerate other beta-lactams
    • Cross-reactivity w/ cephalosporins & carbepenams low (but do not use if hx of anaphylaxis)
  • Aztreonam (monopenam) safe
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11
Q

For penicillin:

  1. Types
  2. Spectrum
  3. Indications
  4. Mechanism
  5. Resistance
  6. Side effects
A
  1. Types: **Penicillin G, benzathine (oral) **& penicillin VK (IV)
  2. Fairly narrow spectrum (bacterial resistance).
  3. Use for primary syphilis & streptococcus pyogenes
  4. Binds PBPs
  5. Beta-lactamase, altered porins, efflux pumps, altered PBPs
  6. Allergies (IgE), c. diff
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12
Q

For anti-stahylococcal (semi-synthetic) penicillins:

  1. Types
  2. Indications
  3. Mechanism
  4. Resistance
A
  1. Types:** Nafcillin** (IV), Oxacillin (IV), Dicloxacillin (PO) (NOD)
  2. S. aureus
  3. Bulky side chains resist penicillinase
  4. Bulkiness prevents entry into GN

NB: MRSA are not susceptible to this class of drugs (make PBP2a).

NB: Nafcillin is secreted biliary; negligible renal clearance.

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13
Q

For amino penicillins:

  1. Types
  2. Indications
  3. Mechanism
  4. Resistance
A
  1. Types:** Ampicillin & Amoxicillin** (IV/PO)
  2. Strep, enterococc, broad GN
  3. Charged amino group increases penetration of porins (vs. penicillin)
  4. Beta-lactamase

NB: Should at beta-lactamase inhibitor (e.g., ampicillin-sulbactam or amoxicillin-cluvulanate –> “turbo amino-penicillins”); expands spectrum to include anaerobes (bacteroides) but causes incr. GI toxicity.

NB2: Amoxicillin has better absorption due to -OH (stable in stomach acid).

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14
Q

For anti-pseudonomal (extended spectrum) penicillins:

  1. Types
  2. Spectrum
  3. Indications
  4. Mechanism
  5. Resistance
  6. Toxicity
A
  1. Types:** Piperacillin-tazobactam, ticarcillin & carbenicillin **(IV/PO)
  2. GP (strep), GNR (E. Coli, Klebsiella), anaerobes, pseudomonas (opportunistic GN)
  3. P. aeruginosa
  4. Charged side chains incr. permeability, PBP binding
  5. Penicillinase sensitive; deactivated by AmpC (inducible beta lactamase)
  6. Platelet dysfunction, hypokalemia
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15
Q

Name the cephalosporins by generation.

A
  • First
    • Cephalexin, cefazolin (Alex & Zola)
  • Second
    • Cefuroxime, cefoxitin & cefotetan (The furry fox in a tin had tea and a tan)
  • Third
    • Ceftriaxone, cefotaxime, cefpodoxime & ceftazidime (Three axes taxed the pod ox a dime)
  • Fourth: Cefepime
  • Fifth: Ceftaroline (Caroline was last)
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16
Q

For the first generation cephalosporins:

  1. Types
  2. Spectrum
  3. Mechanism
  4. Resistance
  5. Indications
A
  1. Cephalexin (PO) & cefazolin (IV)
  2. GP (strep, staph), limited GN (E. Coli, Klebsiella, proteus)
  3. Bind PBPs
  4. Permeability, beta-lactamase, altered PBPs, efflux pumps
  5. Skin & soft tissue infections (not MRSA), perioperative prophylaxis

NB: do not use for enterococci or resistant GP/GNs

17
Q

For the third generation cephalosporins:

  1. Types
  2. Spectrum
  3. Mechanism
  4. Resistance
  5. Indications
A
  1. Ceftriaxone (IV/IM), cefotaxime, cefpodoxime (PO)** **& **ceftazidime **(IV)
  2. GP (strep, staph), GN (E. Coli, Klebsiella, proteus, P. aerug, Enterobac), pseudomonal activity (major incr. in GN, major decr. in GP activity over 2G)
  3. Binds PBPs
  4. Permeability, altered PBPs, efflux pumps
  5. Resistant CAP, meningitis, gonorrhea (ceftriaxone/cefpodoxime), CNS Lyme

NB: Has CNF coverage (use in N. men): the two AXes.

NB2: Do not administer if penicillin allergy.

18
Q

For the second generation cephalosporins:

  1. Types
  2. Spectrum
  3. Mechanism
  4. Resistance
  5. Indications
A
  1. **Cefuroxime, cefoxitin **& **cefotetan **(PO/IV)
  2. GP (strep, staph), GN (E. Coli, Klebsiella, proteus, H. flu), anaerobes (B. frag) (major incr. in GN, minor decr. in GP activity over 1G)
  3. Binds PBPs
  4. Permeability, altered PBPs, efflux pumps
  5. CAP, anaerobes, RTI

NB: Increased beta-lactamase stability.

NB2: Do not rx for prosthetic device infections.

19
Q

For the fourth generation cephalosporin:

  1. Types
  2. Spectrum
  3. Mechanism
  4. Resistance
  5. Indications
A
  1. Cefepime (IV/IM)
  2. GP (strep, staph), GN (best of all gens; better membrane penetration, ampC resistance; E. Coli, Klebsiella, proteus, H. flu, pseudomona), anaerobes (B. frag)
  3. Binds PBPs
  4. Permeability, altered PBPs, efflux pumps
  5. Post-operative CNS infections

NB: Has excellent CNS penetration

20
Q

For the fifth generation cephalosporin:

  1. Type
  2. Spectrum
  3. Mechanism
  4. Indications
A
  1. Ceftaroline (IV/IM)
  2. GP (MRSA), GN (broad)
  3. Increased affinity to PBP2a
  4. MRSA, resistant CAP

NB: Similar to non-pseudomonal 3Gs, but covers MRSA.

NB2: Do not use without ID consult!

21
Q

For ceftriaxone:

  1. Indications
  2. Adjustment
  3. Adverse effect
A
  1. Meningitis & gonorrhea
  2. Not required for renal impairment; has dual biliary and renal excretion (similar to cefotaxime)
  3. Pseudolithiasis (biliary sludge)
22
Q

For carbapenems:

  1. Type
  2. Mechanism
  3. Resistance
  4. Spectrum
  5. Indications
  6. Toxicity
A
  1. Imipenem-cilastatin & meropenem (IV/IM)
  2. No beta-lactam ring, high affinity for PBP2, porin permeable
  3. Alter porins (pseudomonas), carbapenemase (enterobac)
  4. Broadest spectrum of beta-lactam abx; most GPs (except MRSA & E. faecium), GNs (including P. Aerug, even if ESBL, ampC), anaerobes (including bacteriodes)
  5. Broad coverage
  6. Seizures in high doses (pts w/ renal insufficiency; imipenem-cilastatin higher risk)

NB: New Delhi metallo-beta-lactamase-1 (NDM-1) makes bacteria resistant; poor effective therapy

23
Q

For monobactams:

  1. Type
  2. Mechanism
  3. Resistance
  4. Spectrum
  5. Indications
A
  1. Aztreonam
  2. No beta-lactam ring, high affinity for PBP-2, porin permeable
  3. Efflux pumps, ESBLs, ampCs
  4. Only GN (P. aerug, enterobac)
  5. Septic shock to treat tough GNs; with severe penicillin allergy

NB: CNS penetration

NB2: reserved for patients w/ severe penicillin allergy (monobactam = one ring)

24
Q

For ampC beta-lactamase:

  1. Susceptible abx
  2. Expression
  3. Common organisms
  4. Treatment class
A
  1. 3G, aztreonan, beta-lactamase inhibitors
  2. Chromosomal & inducible; if organism is resistant to cephamycins, suggests ampC expression
  3. Serratia, Pseudomonas, Acinetobacter, Citrobacter, and Enterobacter (SPACE)
  4. Carbapenems
25
Q

For extended spectrum beta-lactamases (ESBLs):

  1. Susceptible abx
  2. Expression
  3. Treatment class
A
  1. Penicillins, 1-3G, aztreonam (beta-lactamase inhibitors may still work)
  2. On chromosome or plasmid, thus many different types
  3. Carbapenem
26
Q

For vancomycin:

  1. Abx class
  2. Spectrum
  3. Mechanism
  4. Resistance
  5. Indications
A
  1. Glycopeptide (not beta-lactam)
  2. GP bacteria resistant to other abx (e.g., MRSA); cannot enter porins of GN due to size
  3. Prevents cell wall cross-linking by interacting w/ D-ala-D-ala pentapeptide terminus
  4. Alternative D-ala-D-lac peptide (VISA/VRSA)
  5. MRSA (IV), resistant S. pneumoniae, enterococci (not VRE), listeria/bacillus/clostridium spp.
27
Q

Describe the indications for oral vancomycin.

A

Resistant pneumococcal meningitis.

Severe C. difficile colitis (PO/rectal).

NB: PO vancomycin not absorbed from gut into systeic circulation.

28
Q

Describe Red Man Syndrome.

A

Adverse reaction associated with vancomycin.

If vancomycin introduced too quickly (i.e., rapid infusion), body may release histamines –> low BP, feeling hot, thrombophlebitis.

Resolve by slowing infusion rate.

29
Q

What is the pharmacology of vancomycin?

A
  • ~55% bound to protein; >90% eliminated renally
  • Dosed by weight; adjustment necessary for pts w/ renal insufficiency/hemodialysis.
  • Trough levels monitered to ensure adequate serum concentrations, prevent toxicity.

NB: Can enter CNS.

Microbiology & Infectious Diseases (26 decks)

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