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CC Internal Med > Antibiotics > Flashcards

Antibiotics Flashcards

1
Q

Abscesses: what type of environment? Which class not effective?

A

acidic

aminoglycosides

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2
Q

Which antibiotics have such good

bioavailability that po = IV availability? (5)

A 
– Clindamycin po = IV
– Fluoroquinolones po = IV
– Septra po = IV
– Tetracyclines po = IV
– Metronidazole po = IV
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3
Q

Time-dependent
antibiotics
(Concentration-INDEPENDENT - dep on amount of time above MIC) (7)

A 
B-lactams (Penicillins, Cephalosporins, carbapenems)
Vancomycin
Macrolides
Clindamycin
Tetracyclines
Linezolid
Quinipristin/dalfopristin
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4
Q

Concentration-dependent

antibiotics (hit hard, fast, high) (3)

A

Aminoglycosides
Fluoroquinolones
Metronidazole

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5
Q

Bacteriostatic vs. bactericidal

A

– Inhibition of cell wall synthesis or protein
synthesis = cidal
– Changes in bacterial physiology = static
– Depends on drug concentration

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6
Q

Mech of action: inhibit cell wall synth (4)

A

Vancomycin
Bacitracin
Penicillins
Cephalosporins

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7
Q

Mech of action: decrease cell wall integrity (1)

A

b-lactamases

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8
Q

Mech of action: inh DNA synth (1)

A

metronidazole

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9
Q

Mech of action: inh DNA gyrase

A

Quinolones

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10
Q

Mech of action: inh RNA polymerase

A

Rifampicin

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11
Q

Mech of action: inh protein synth (50S) (3)

A

erythromycin
chloramphenicol
clindamycin

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12
Q

Mech of action: inh protein synth (30S) (2)

A

tetracyclines

streptomycin

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13
Q

Mech of action: inh folic acid metabolism

A

sulfonamides

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14
Q

B-lactam group: 4 members & mech

A
  • Penicillins
  • Cephalosporins
  • Carbapenems
  • Monobactam

Inhibition of cell wall synthesis by binding to penicillin-binding
proteins

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15
Q

B-lactam resistance mechs (3)

A

– Inactivation of antibiotic (penicillinase, or

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16
Q

Penicillin: 2 types

A

– G procaine (IV)
– G benzathine (IM)
• Penicillin G benzathine : long half life and
elimination
– use is limited to treatment of syphilis, and sometimes
rheumatic heart disease
– V (oral/po)

(Used to be good against Gram+ including anaerobes, but S. aureus is now largely resistant)

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17
Q

Penicillin for Tx S. aureus

A

Penicillinase-resistant:

Cloxacillin (gain in S. aureus activity = loss of anaerobic activity)

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18
Q

Penicillin with expanded Gram- coverage (E. coli) (2)

A

Aminopenicillins:
– Ampicillin IV
– Amoxicillin (Amoxil) po

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19
Q

Penicillin with Pseudomonas aeruginosa coverage (2)

A

– Ticarcillin

– Piperacillin

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20
Q

Penicillin / B-lactamase inh combinations (3)

A

• Amoxicillin-clavulanic acid
– Clavulin po, Augmentin (IV/po)

• Ticarcillin-clavulanic acid
– Timentin IV

• Piperacillin-tazobactam
– Zosyn IV, Tazocin IV, Pip/tazo IV

Common side effect: diarrhea due to B-lac inh

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21
Q

Penicillin / B-lactamase inh: coverage

A

BROAD SPECTRUM
– All combinations are active against:
• S. aureus
• Most gram-positive organisms including Enterococcus and Listeria
spp
• Most gram-negative respiratory pathogens (Haemophilus and
Moraxella spp)
• Most gram-negative enteric bacteria
• Most anaerobes (gram-positive and gram-negative)

– Timentin and Pip/tazo
• Active against ALL above BUT ALSO Pseudomonas spp

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22
Q

Coverage: Penicillin G

or V

A

Gram-positive (GAS, S.pneumoniae)
Anaerobes and some Gram-negative
(N.meningitidis)

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23
Q

Coverage: Cloxacillin

A

Gram-positive (GAS, S.aureus)

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24
Q

Coverage: Amoxicillin & Ampicillin

A

Gram-positive (GAS S pneumoniae), Better Gram-negative coverage

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25
Q

Coverage: Ticarcillin & Piperacillin

A

Gram-positive but much better Gram-negative coverage – including
P.aeruginosa

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26
Q

Coverage: Amoxicillin-clavulanic acid & Piperacillin-tazobactam

A

Good Gram-positive coverage –

including S.aureus, increased Gram-negative coverage and anaerobes

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27
Q

Important property of cephalosporins

A

Increased stability against beta-lactamases

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28
Q

1st gen cephalosporins (3)

A

IV: Cefazolin (Ancef)
PO: Cephalexin (Keflex), Cefadroxil (Duricef)

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29
Q

2nd gen cephalosporins (3)

A

IV: Cefuroxime (Zinacef)
PO: Cefuroxime axetil (Ceftin), Cefprozil (Cefzil)

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30
Q

3rd gen cephalosporins (4)

A

IV: Ceftriaxone (Rocephin), Cefotaxime (Claforan), Ceftazidime (Fortaz, Tazicef)
PO: Cefixime (Suprax)

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31
Q

4th gen cephalosporin (1)

A

Cefipime (Maxipime)

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32
Q

1st gen cephalosporins: activity

A

Excellent against Gram-positive – including S.aureus and GAS
Limited against Gram-negative mainly due to emergence of resistance
No anaerobic activity

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33
Q

2nd gen cephalosporins: activity

A

Excellent against Gram-positive
Increased coverage of Gram-negative, mainly respiratory flora
Coverage of Enterobacteriaceae
No anaerobic coverage

Note: 2nd gen cephamycins (Cefoxitin, Cefotetan): Less Gram positive coverage, Good Gram-negative coverage (not P.aeruginosa), * Anaerobic coverage (Bacteroides)

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34
Q

3rd gen cephalosporins: activity

A 
Less optimal Gram-positive coverage
Excellent Gram-negative coverage
No P.aeruginosa coverage (EXCEPT FOR CEFTAZIDIME)
BBB penetration (IV formulation)
No real anaerobic coverage
Cefixime: poor bioavailability
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35
Q

4th gen cephalosporins: activity

A

Good Gram-positive coverage
Good Gram-negative coverage including P.aeruginosa
No anaerobic coverage

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36
Q

Cephalosporins: trends in Gram + and - coverage from 1st to 4th gen

A

Gram+ decreasing from 1st to 3rd, increasing from 3rd to 4th

Gram- increasing from 1st to 4th

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37
Q

Cephalosporins with coverage against Pseudomonas, Campylobacter

A

Pseudomonas: ceftazidime (the only 3rd gen) and 4th gen

Campylobacter: no coverage

(both are Gram-)

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38
Q

Cephalosporins with coverage against Enterococcus and Listeria

A

None!

both are Gram+

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39
Q

Carbapenems (4)

A

Meropenem
Imipenem
Ertapenem
Doripenem

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40
Q

Monobactams (1)

A

Aztreonam

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41
Q

Carbapenems: coverage

A 
BROAD SPECTRUM
– Like BROAD SPECTRUM beta-lactams/beta-
lactamase inhibitor combinations
• Gram-positives (MSSA), gram-negative,
anaerobes
• Usually resistant to beta-lactamases

(Recent emergence of carbapenemases in
gram-negative enteric rods
– Emerging problem)

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42
Q

Imipenem, meropenem coverage

A

Excellent activity against Gram-positive (less
against Enterococcus faecium)
Excellent activity against Gram-negative –
including P.aeruginosa
Excellent anaerobic activity
Intrinsic resistance: Stenotrophomonas
maltophilia, C.jeikeium, C.difficile, atypical
bacteria (Mycoplasma, Chlamydia, Legionella),
B.pertussis
Good BBB penetration

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43
Q

Ertapenem coverage

A

Good activity against Enterobacteriaceae and
anaerobes
No activity against P.aeruginosa,
Acinetobacter, PRSP and enterococci

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44
Q

Aztreonam coverage

A

Same as aminoglycosides i.e. aerobic Gram-negative

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45
Q

Monobactams: coverage

A

NARROW SPECTRUM
– Gram-negative aerobic bacteria
• IV formulation
• Rarely used

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46
Q

Adverse reactions

All beta-lactams) (3 mild, 2 serious

A

Mild side effects
– GI upset
– Diarrhea (beta-lactamase inhibitors; cefixime/Suprax)
– Drug induced neutropenia

Serious side effects
– Seizures
• All beta-lactams lower seizure threshold, some more than others (e.g. imipenem)
– Anaphylaxis
• If anaphylaxis with one penicillin, high risk of reacting to another
penicillin – less risk with cephalosporins
• 10% cross-reactivity between penicillins and carbapenems

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47
Q

Which beta-lactams cross the BBB

appreciably? (5)

A 
– Penicillin IV (high dose)
– Ampicillin IV (high dose)
– Third generation cephalosporins IV (high dose)
– Cefepime
– Carbapenems
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48
Q

Which beta-lactams have activity against MSSA? (5)

A

– Cloxacillin po/IV (and methicillin)
– b-lactam/b-lactamase combinations (po/IV)
– 1st and 2nd generation cephalosporins po/IV
• 3rd generation IV NOT that good – just OK
– Cefepime
– Carbapenems

49
Q

Which beta-lactams have activity against

Pseudomonas spp? (5)

A 
– Ticarcillin and Piperacillin (IV)
– Timentin and Pip/tazo (IV)
– Ceftazidime (IV)
– Cefepime (IV)
– Carbapenems (IV)
50
Q

Which beta-lactams have activity against

anaerobes? (3)

A

– Penicillin (po/IV)
– All b-lactam/b-lactamase combinations (po/IV)
– Carbapenems (IV)

51
Q

Glycopeptides (2)

A

Vancomycin

Teicoplanin

52
Q

Glycopeptides mech

A 
• Inhibition of cell wall synthesis
• Inhibit the CROSS-LINKING of peptidoglycan
• Resistance:
– Enterococcus spp (VRE): Van gene
• Decreased affinity for vancomycin
– S.aureus (VISA; VRSA):
• Increased thickness of cell wall
– Increased D-ala-D-ala: traps glycopeptides
• Emerging problem
– Time-dependent killing
• some Post Antibiotic Effect
53
Q

Vancomycin coverage

A

Possesses only Gram-positive activity –
including anaerobic Gram-positive
Very good activity against C. diff (oral treatment)

54
Q

Vancomycin: administration

A

• No oral absorption
• Available as oral, IV, intraperitoneal,
intrathecal or intraventricular administration
• No IM: pain and local necrosis
• Renal excretion
• BBB penetration, mainly with inflammation
• Need higher levels to penetrate BBB, bone and cartilage, heart tissue
• Need higher levels when dealing with MRSA

55
Q

Vancomycin: adverse rxs (2)

A

• Nephrotoxicity
– Usually with accumulation (high trough levels)
– when co-administered with other nephrotoxic
drugs
– Therapeutic drug monitoring to prevent this

• When administered over short period (<1hr)
– Histamine release (Red-man syndrome)
• Flushing
• Hives
• Even hypotension
56
Q

Macrolides (3)

A 
– Erythromycin (IV/po)
• Erythromycin estolate (po)
– Clarithromycin (po)
• Biaxin
– Azithromycin (IV/po)
• Zithromax
(Newer macrolides have better PK
parameters, e.g. Azithromycin has a long half life; 
• Time-dependent killing
• Azithromycin possesses some Post
Antibiotic Effect)
57
Q

Ketolides (1)

A

– Telithromycin (po)

• Ketek

58
Q

Macrolides/ketolides: Mechanisms of action and resistance

A

• Inhibition of protein synthesis
• Ketolides: increased affinity for target sites
– less resistance when compared to macrolides

• Resistance:
– Modification of target site (erm)
– Efflux pump (mef)

• Most gram-negatives: intrinsic resistance to
macrolides
– no penetration into gram negative bacteria
– Exceptions: Campylobacter spp, Bordetella pertussis, some
Haemophilus spp

59
Q

Antibacterial spectrum: Macrolides/Ketolides

A 
• Essentially:
– Gram-positives
• S. pneumoniae (if S)
• Group A Streptococcus (if S)
– Gram-negatives
• Campylobacter spp
• Bordetella pertussis
– Atypical bacteria
• Mycoplasma spp, Chlamydia spp, Clamydophila spp
– Non-tuberculous mycobacteria
• Clarithromycin, azithromycin
60
Q

Erythromycin & clarithromycin coverage

A

OK activity against S.aureus sensitive to
macrolides, GAS, S.pneumoniae when
sensitive
Alternative for penicillin for allergic patients
Atypical bacteria and B.pertussis

61
Q

Azithromycin coverage

A

Same as other macrolides except (1) more potent, (2) coverage of H.influenzae
Azithromycin also has some Gram-negative coverage

62
Q

Telithromycin coverage

A 
Same as erythromycin but better coverage
against Gram-positive
Not active against S.aureus resistant to
erythromycin
Not active against Enterobacteriaceae
63
Q

Do macrolides cross the BBB?

A

No

64
Q

Adverse reactions: erythromycin

A

– GI upset with erythromycin (cramps/nausea)
• Because it causes the GI tract to contract it can be used to treat GI reflux in children
– QT prolongation with erythromycin
– Pyloric stenosis if erythromycin is given to
neonates

65
Q

Adverse reactions: telithromycin

A
  • severe liver toxicity
  • exacerbations of myasthenia gravis

Since 2007: only licensed for community acquired
pneumonia
• Only as an alternative drug
• BLACK BOX warning from the FDA
• Avoid use in myasthenia gravis patients

66
Q

Aminoglycosides (5)

A 
Gentamicin
Tobramycin
Amikacin
Streptomycin
Paromomycin
67
Q

Mechanisms of action and resistance: Aminoglycosides

A 
• Inhibit protein synthesis
– Act at the level of the ribosomes
• Resistance:
– Efflux pump
– Modification of target (mutated ribosome)
– Enzymatic inactivation of antibiotic
• Bactericidal and concentration-dependent
with Post Antibiotic Effect
68
Q

Antibacterial spectrum: Aminoglycosides

A

• GRAM-NEGATIVE!
• Including Pseudomonas spp
• Except Salmonella spp, Neisseria spp
– Some have activity against TB and non-TB
mycobacteria
– Paromomycin has anti-parasitic activity (Giardia lamblia)

69
Q

Coverage: Gentamicin, Tobramycin, Amikacin

A

Aerobic or facultative Gram-negative bacteria
– including P aeruginosa

Synergy with cell-wall agents against Grampositive
NO anaerobic coverage
NO Gram-positive coverage
Amikacin best against MAI and other atypical
mycobacteria

70
Q

Paramomycin coverage

A

Only PO administration – good against

G.lamblia, E.histolytica

71
Q

Streptomycin coverage

A

Best against M.tuberculosis, Y.pestis,

F.tularensis

72
Q

Spectinomycin coverage

A

Some use against N.gonorrheae

73
Q

Aminoglycosides: oral aborption? Conc- or time-dep killing? BBB penetration? Activity in acidic environ?

A 
• NO oral absorption
• Concentration-dependent killing
• No BBB penetration
• Poor activity in acidic environment
– Not good when an abscess is present
74
Q

Adverse reactions: Aminoglycosides (3)

A

• Renal toxicity:
– Associated with high accumulated levels (High trough levels)
– Increased if co-administered with other nephrotoxic drugs
– Reversible

• Vestibular and cochlear toxicity:
– Associated usually with prolonged use
– Tinnitus is the first problem sign
– Irreversible hearing loss

• Muscular blockade:
– Should be avoided in people with neuromuscular diseases (Botulism, Duschenne muscular dystrophy, myasthenia gravis etc)

75
Q

Fluoroquinolones: 3 to remember

A
  • Ciprofloxacin po/IV (Cipro) = 2nd gen
  • Levofloxacin po/IV (Levaquin) = “The respiratory quinolone” = 3rd gen
  • Moxifloxacin po (Avelox) = 4th gen
76
Q

Mechanisms of action and resistance: Fluoroquinolones

A

• Inhibition of bacterial DNA synthesis
– DNA gyrase & topoisomerase II/IV
• Resistance:
– Modification of target enzymes
– Decreased bacterial permeability (porins)
– Efflux pump
• Concentration-dependent killing with short Post Antibiotic Effect

77
Q

Antibacterial spectrum: Fluoroquinolones: trends from 1st to 4th generation for coverage against (1) S. pneumoniae, (2) MSSA, (3) enteric Gram- rods, (4) Pseudomonas spp, (5) Atypicals

A

1st gen: Very limited Gram-negative activity
Not suitable to treat systemic infections
Not used in clinical practice

2nd to 4th gen: increasing coverage against (1) and (2), same coverage against (3) and (5), decreasing coverage against (4)

4th gen only has coverage against Enterococcus faecalis and anaerobes

78
Q

2nd gen fluoroquinolones Ciprofloxacin, Ofloxacin coverage

A

Best against P.aeruginosa. Good coverage of Gram-negative
Poor Gram-positive coverage
Improved PK parameters, enables treatment of systemic infections

79
Q

2nd gen fluoroquinolone Norfloxacin coverage

A

Better coverage of Gram-negative – including P.aeruginosa

No anaerobic activity, poor Gram-positive activity

80
Q

3rd gen fluoroquinolones Levofloxacin
Grepafloxacin
Sparfloxacin
Gemifloxacin coverage

A

Increased coverage of Gram-positive – mainly S.pneumoniae
Good coverage of atypical bacteria (Moraxella, Legionella, Chlamydia)
Some activity against S.aureus
Gemifloxacin: best of the group against S.pneumoniae

81
Q

4th gen fluoroquinolone Moxifloxacin coverage

A

Excellent Gram-positive (including S.pneumoniae) and Gram-negative
coverage (+/- against P.aeruginosa)
Anaerobic activity
Active against Enterococcus faecalis

82
Q

4th gen fluoroquinolone Trovafloxacin coverage

A

Excellent P.aeruginosa activity
Best anaerobic coverage
Fatal liver toxicity

83
Q

Fluoroquinolones: oral absorption? What causes decreased bioavailability? BBB penetration?

A
  • Rapid and good oral absorption (Oral = IV availability)
  • Decreased bioavailability with milk and calcium
  • Poor BBB penetration
84
Q

Adverse reactions: Fluoroquinolones (main adverse rxs (2), main contraindications (2))

A 
• Not approved for use in paediatrics
– growth cartilage damage (e.g. beagles)
– This has not been seen in humans
– Is used in children when NEEDED
• Well tolerated, mainly GI upset
• Prolonged QT interval
• Pregnancy: Contraindicated
85
Q

Sulfonamides (3)

A

Trimethoprim-sulfamethoxazole (Septra)
Sulfadiazine
Dapsone

86
Q

Sulfonamides: mech and resistance

A

• Bacteriostatic, interfere with folic acid
pathway
• Inhibits bacterial dihydrofolic acid

• Resistance:
– Modification of target
– Decreased permeability

87
Q

Trimethoprim-

Sulfametoxazole: coverage

A

Broad spectrum – all bacteria requiring
endogenous folic acid synthesis

Gram-positive and Gram-negative including
Enterobacteriaceae, Shigella, S.maltophilia,
B.cepacia
(No activity against Group A Streptococcus, and Enterococcus spp)

Chlamydia, Nocardia
Pneumocystis jeroveci, Toxoplasma (anti-parasitic activity) - But most have developed resistance

Enterococcus intrinsically resistant

88
Q

Sulfonamides: usual route of administration? Oral bioavailability? BBB penetration? Drugs of choice for which specific infections? (2)

A

• Usually administered PO (Oral = IV availability)
– IV formulation for Septra exists
• BBB penetration
– But there are better drugs for meningitis
– Worry is increasing resistance of many bacteria

• Drugs of choice for:
– Toxoplasma gondii infections
– Pneumocystis jiroveci

89
Q

Adverse reactions: Sulfonamides (5) and 1 contraindication

A 
• GI reactions
• Skin rashes: including Stevens-Johnson
• Kernicterus in children < 1 month of age
– Sulfa drugs are highly protein bound
– Bilirubin displacement from albumin
• Hemolysis in G6PD deficient people
• Allergy and Anaphylaxis
• Pregnancy: Contraindicated
90
Q

Tetracyclines (3) and Glycylcycline (1)

A

• Tetracyclines
– Tetracycline (po/IV)
– Doxycycline (po)
– Minocycline (Topical only; acne treatment)

• Glycylcycline
– Tigecycline (IV)

91
Q

Tetracyclines and Glycylcycline: mech and resistance

A
  • Inhibition of protein synthesis in ribosome and mitochondria
  • Time-dependent killing
  • Post Antibiotic Effect

• Resistance:
– Efflux pump
– Ribosomal protection through inactivation by specific enzymes
– Tigecycline: increased affinity able to overcome resistance

92
Q

Tetracycline coverage

A 
Broad spectrum
Anaerobic Gram-positive and Gram-negative
bacteria
Atypical bacteria and intracellular pathogens,
Vibrio sp., spirochetes
Activity also against parasites
BUT S.pneumoniae, N.gonorrheae now
resistant
93
Q

Doxycycline coverage

A

Same spectrum as tetracycline
Better PK parameters

Doxycycline ONLY (no other tetracyclines): Anti-malarial prophylaxis

94
Q

Tigecycline coverage

A

Same as tetracyclines but remains active against
organisms resistant to tetracyclines
Active against MRSA, VRE, PRSP

95
Q

Tetracyclines: spectrum

A

– Gram negative enteric rods
– Anaerobes
– Atypical bacteria

96
Q

Tigecycline: spectrum

A 
– Gram negative enteric rods
• Even those resistant to tetracyclines
• Multiresistant Enterobacteriaceae
– Gram positive
• MRSA, VRE, Penicillin-resistant S. pneumoniae
– Anaerobes
– Atypical bacteria
97
Q

Tetracyclines and tigecycline: adverse rxs (2)? Contraindications (2)? Oral bioavail?

A 
• Rare anaphylaxis
• Photosensitivity
– Rash (doxycycline)
• Not recommended in children under 8 years of age: discoloration of permanent teeth
– Mostly seen with tetracycline
• Tigecycline: not approved for < 18 years of age (No good studies in adolescents)
• Pregnancy: Contraindicated
• Oral = IV availability
98
Q

Lincosamides (1)

A

Clindamycin

99
Q

Mechanisms of action and resistance: Clindamycin

A

• Inhibition of protein synthesis

• Resistance:
– Similar to macrolides

• Bacteriostatic time-dependent activity

100
Q

Coverage: Clindamycin

A 
Good Gram-positive coverage, including
S.pneumoniae and S.aureus (ONLY if erythromycin S - resistance is similar to macrolides)
Good anaerobic activity
No Gram-negative coverage
No activity against Enterococcus sp.
101
Q

Clindamycin: oral bioavail? BBB penetration? How is it cleared? Where does it concentrate well?

A
  • Can be administered IM - Oral = IV/IM availability
  • No BBB penetration
  • Excellent concentration in bone
  • Hepatobiliary clearance
102
Q

Adverse reactions: Clindamycin

A

• Usually well tolerated
• May cause moderate diarrhea
• Associated with C.difficile colitis
– like most other antimicrobials

103
Q

Metronidazole: used since 1950s for what? “Non-bacterial” application?

A

• Used since the 1950’s for bacterial vaginosis
• Activity against protozoa and parasites
discovered much more recently
• Anti-inflammatory effects at the level of the
colon
– Irrelevant to antimicrobial activity
– Used to “cool off” IBD exacerbations

104
Q

Mechanisms of action and resistance: Metronidazole (Flagyl)

A

• Toxic to bacteria
– via production of free-radicals
• Very rapidly bactericidal, concentration-dependent

• Resistance:
– Very rare
– Decreased permeability
– Mutated targets in bacteria?

105
Q

Metronidazole coverage

A

THINK: Anaerobes (gram positive and gram negative)
Clostridium difficile
ALSO THINK: Antiparasitic activity (Giardia lamblia, Entamoeba histolytica)

Very good anaerobic activity
Propionebacterium and Actinomyces most
often resistant
Good activity against C.difficile, G.vaginalis,
H.pylori
106
Q

Metronidazole: route of admin? Metabolism/excretion? Oral bioavail?

A 
• Available forms
– Oral (po)
– IV
– Topical
– Rectal (pr)

• Hepatic metabolism
– Avoid alcohol: disulfiram reaction
– Renal excretion

• Oral = IV availability

107
Q

Adverse reactions: Metronidazole (Flagyl) (3)

A 
• Well tolerated except GI upset
– Metallic taste in mouth
• CNS adverse effects after prolonged or
high-dose administration
– Headache, confusion
• Disulfiram effect
–With alcohol
108
Q

Rifamycins (2)

A

Rifampin

Rifabutin

109
Q

Rifamycins: mech and resistance

A 
• Inhibition of bacterial
RNA synthesis
– RNA polymerase
• Resistance:
– Multiple mutations in
gene coding beta-subunit of RNA polymerase
– Decreased permeability
110
Q

Antibacterial activity: Rifamycins

A 
• On their own, rifamycins induce RAPID
resistance
– Never used alone to treat infections
• Always with other antibiotics to buffer
resistance

– Can be used alone as prophylaxis
• Against developing meningitis from
N.meningitides, and H. influenzae

111
Q

Antibacterial spectrum: Rifamycins

A

• THINK:
– Treatment:
• TB
• non-TB mycobacteria

– Post-exposure prophylaxis:
• N. meningitides (meningitis and/or meningococcemia)
• H. influenzae (meningitis)

112
Q

Rifampicin coverage

A

Better against M.tuberculosis than rifabutin
Active against M.leprae
Bactericidal against S.aureus
Should not be used as monotherapy because
of rapid development of resistance
Post-exposure prophylaxis: N.meningitidis and
H.influenzae (invasive disease)

113
Q

Rifabutin coverage

A

More lipophilic: better activity against M.avium
intracellulare
Otherwise same as rifampin

114
Q

Rifamycins: route of admin? Metabolism and resulting interactions?

A

• Rifampin: available only as oral form
– Activity is affected by food
• Rifabutin: less affected by food

• MAJOR drug interactions
– Both are metabolized in the liver and
induce CYP-450 enzymes

115
Q

Rifamycins: Adverse rxs (4)

A

• Mainly GI
– Nausea
– Increase in liver enzymes

• Skin rashes

• Rifampin:
– Orange-red colouration of body fluids (urine, tears)
• May permanent contact lenses

• Rifabutin:
– Bronze discolouration of skin
– Violet-red colouration of urine

116
Q

Nitrofurantoin: use, mech, resistance

A

• Only used for UTI treatment and
prophylaxis
– Therapeutic concentrations achieved
ONLY in urine

  • Bacteriostatic (low dose) and bactericidal (high dose)
  • Unclear mode of action

• Resistance:
– Decreased activity of nitrofurane reductase

117
Q

Nitrofurantoin: coverage

A

THINK: treatment of uncomplicated UTI

Active against Enterobacteriaceae
Active against some Enterococcus sp,
S.aureus and coagulase-negative
staphylococci (S.saprophyticus)

118
Q

Adverse reactions: Nitrofurantoin (4)

A 
• Mainly minor GI disturbances
• 1/5000 pulmonary syndrome with:
– Fever
– Chills
– Difficulty breathing
– Cough
– May be fatal
• Stevens-Johnson Syndrome
• Hemolytic anemia
119
Q

Antibiotics specifically produced for
multiresistant gram-positive bacteria
(AGAINST MRSA AND/OR VRE)

A

• Oxazolidinones
– Linezolid

• Streptogramins
– Quinipristin/Dalfopristin

• Daptomycin

CC Internal Med (6 decks)

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