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RACP Written 2018 > Infectious Diseases - Antibiotics: Mechanisms of Action > Flashcards

Infectious Diseases - Antibiotics: Mechanisms of Action Flashcards

1
Q

Which antibiotic classes (and which antibiotics) are inhibitors of cell wall synthesis?

A

Beta-Lactams

  • penicillins
  • cephalosporins
  • carbapenems
  • monobactams

Glycopeptides

  • Vancomycin
  • Teicoplanin

Others:

  • cycloserine
  • bacitracin
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2
Q

Which antibiotic classes are inhibitors of protein synthesis via the 30s ribosomal subunit?

A

Aminoglycosides
Tetracyclines
Tigecycline

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3
Q

Which antibiotic classes are inhibitors of protein synthesis of the 50s ribosomal subunit?

A 
Chloramphenicol
Lincosamides
Macrolides
Fusidic acid
Streptogramin
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4
Q

Which antibiotic classes are inhibitors of nucleic acid synthesis?

A

Block folic acid synthesis:

  • trimethoprim
  • sulfonamides

Block DNA gyrase:
- fluoroquinolones

RNA polymerase inhibition
- rifamycins

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5
Q

How do they work: Penicillins

A

Penicillins are a beta-lactam and inhibit cell wall synthesis

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6
Q

How do they work: Vancomycin

A

Vancomycin is a glycopeptide and inhibits cell wall synthesis

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7
Q

How do they work: Cycloserine

A

Inhibits cell wall synthesis

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8
Q

How do they work: Aminoglycosides

A

Inhibit protein synthesis by 30s ribosomal subunit

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9
Q

How do they work: Cephalosporins

A

Cephalosporins are a beta lactam and inhibit cell wall synthesis

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10
Q

How do they work: Teicoplanin

A

Teicoplanin is a glycopeptide and inhibits cell wall synthesis

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11
Q

How do they work: tetracyclines?

A

Inhibit protein synthesis via 30s ribosomal subunit

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12
Q

How do they work: Carbapenems

A

Carbapenems are a beta lactam and inhibit cell wall synthesis

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13
Q

How do they work: Bacitracin

A

Inhibit cell wall synthesis

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14
Q

How do they work: Chloramphenicol

A

Inhibit protein synthesis via the 50s ribosomal subunit

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15
Q

How do they work: monobactams

A

Monobactams are a beta lactam and inhibit cell wall synthesis

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16
Q

How do they work: Macrolides

A

Inhibit protein syntheis via 50s ribosomal subunit

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17
Q

How do they work: Trimethoprim

A

Inhibit nucleic acid synthesis by blocking FOLIC ACID synthesis

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18
Q

How do they work: Fluoroquinolones

A

Inhibit nucleic acid synthesis by blocking DNA gyrase

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19
Q

How do they work: Clindamycin

A

Inhibit protein syntheis via 50s ribosomal subunit

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20
Q

How do they work: sulfonamides

A

Inhibit nucleic acid synthesis by blocking FOLIC ACID synthesis

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21
Q

How do they work: fusidic acid

A

Inhibit protein syntheis via 50s ribosomal subunit

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22
Q

How do they work: rifamycins

A

Inhibit nucleic acid syntheis by blocking RNA polymerase

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23
Q

How do they work: colistin

A

Inhibit cell membrane FUNCTION

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24
Q

How do they work: polyene antifungal drugs

A

Inhibit cell membrane FUNCTION

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25
Q

Which antibiotics work by inhibiting cell membrane FUNCTION?

A

Colistin

Polyene antifungal drugs

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26
Q

How do beta lactams work?

A

Gram positives have a PBP on their outer surface. Penicillins bind to PBPs to interfere with cell wall peptidoglycin synthesis

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28
Q

Why do enterococcus have a natural resistance to penicillins?

A

Enterococcus has a different PBP (although amoxycillin can be used because it has a different binding site)

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30
Q

What are the narrow spectrum penicillins?

A 
Penicillin V (phoxymethylpenicillin)
Penicillin G (benzylpenicillin)
Procaine penicillin
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32
Q

What do narrow spectrum penicillins target?

A

Gram positives: strep pneumo and viridans, and enterococcus FAECALIS

Gram negative:
N meningitidis
Syphilis
Gonorrhoea

Ben pen covers H influenzae

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34
Q

Which are the anti-staph penicillins?

A

Flucloxacillin

Dicloxacillin

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35
Q

What does broad spectrum penicillin cover?

A

All gram positives INCLUDING enterococcus EXCEPT FAECIUM

NOT MRSA

Pseudomonas and gram negatives covered.

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36
Q

What are the first generation cephalosporins?

A

IV: cephazolin
Oral: Cephalexin, cefadroxil

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37
Q

What are the 2nd gen cephalosporins?

A

IV: cefuroxime
Oral: cefaclor, cefuroxime

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38
Q

What are the 3rd gen cephalosporins?

A

IV: cefotaxime, cefriaxone
Oral: cefixime

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39
Q

What are the 4th gen cephalosporins?

A

IV cefepime

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40
Q

What are the 5th gen cephalosporins?

A

IV ceftaroline

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41
Q

What do cephalosporins cover?

A

1st gen is gram positives

2nd gen is gram positives plus respiratory gram negatives, and also against bacteroides

3rd gen has both gram negative and gram positive cover.
They also have some cover for H influenza and Klebsiella
And have better activity against shigella and salmonella

4th gen have both gram positives and gram negative INCLUDING PSEUDOMONAS

5th gen covers MRSA with enhanced activity against strep and enterococcus

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42
Q

What do cephalosporins do badly?

A

Chlamydia
Mycoplasma
Listeria

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43
Q

When might ceftriaxone be used in IE?

A

Used synergistically if not tolerating aminoglycosides

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44
Q

Side effects of cephalosporins?

A

Common: n+v, diarrhoea

Rare: neurotoxicity, renal impairment, blood dyscrasia

Immune: eosinophilia, SJS, TEN, AIN, arthritis

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45
Q

How do Carbapenems work? And what are the three we use?

A

Act with high affinity for multiple PBPs and stability against most beta lactamases including Class A ESBL and class C beta lactamases (AmpC)

Imipenem
Meropenem
Ertapenem

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46
Q

Of the carbepenems which has the best gram positive cover?

A

Imipenem

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47
Q

How do glycopeptides work and what are the two we have?

A

Bind to d-alanyl-D-alynine moieties to inhibit final stage of peptidoglycan synthesis

Teicoplanin
Vancomycin

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48
Q

What do glycopeptides kill?

A

ONLY gram positives EXCEPT listeria

examples of glycopeptides:
Teicoplanin
Vancomycin

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49
Q

Common side effects after glycopeptides

A

(teicoplanin / vancomycin)

  • Nephrotoxicity (vanc causes interstitial nephritis)
  • Immune mediated thrombocytopenia, neutropenia
  • ototoxicity
  • multi organ hypersensitivity
  • red man syndrome
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50
Q

Of the carbapenems which has the best gram negative cover?

A

Meropenem

51
Q

Of the carbapenems which is NOT good against pseudomonas?

A

Ertapenem

52
Q

Mechanism of aztreonam?

A

Inhibits Cell wall synthesis by binding to PBP3 of gram NEGATIVE

53
Q

Side effects of Aztreonam?

A 
GIT
Taste
C diff
Hepatitis 
Neutropenia
Thrombocytopenia

mech: Inhibits Cell wall synthesis by binding to PBP3 of gram NEGATIVE

54
Q

Name the aminoglycosides

A

IV: amikacin, gentamicin, streptomycin, tobramycin

Oral: neomycin

55
Q

How do aminoglycosides work?

A

(amikacin, gentamicin, streptomycin, tobramycin)
Bind IRREVERSIBLE to 30s ribosomal subunit

Is rapidly bactericidal due to sudden release of toxic proteins

56
Q

What DONT carbapenems cover?

A 
Stenotrophomonas multophila
Burkholderia
MRSA
Enterococcus 
Pseudomonas containing new KPC mutation
57
Q

What precautions for aminoglycosides?

A 
(amikacin, gentamicin, streptomycin, tobramycin)
Neuromuscular disease (ie myasthenia gravis)

Hypocalcaemia

Mutation in mitochondrial DNA A1555g (increases risk of ototoxicity)

58
Q

What precautions for carbapenems?

A
  • avoid treating with valproate (lowers valproate level)

- imipenem and ertapenem are contraindicated in meningitis due to seizures

59
Q

What to aminoglycosides cover?

A

(amikacin, gentamicin, streptomycin, tobramycin)
All gram negative except:

Aeromonas
Moraxella
H influenza
Pasturella
Salmonella and shigella
Stenotrophomonas
60
Q

What is Red Man Syndrome

A

Histamine release mediated reaction to glycopeptides like vancomycin

61
Q

Mechanism of Fosfomycin?

When is it used?

A

Irreversible blockage of MurA enzyme (enzyme in peptidoglycan synthesis) which disrupts Cell wall synthesis

It also decreases bacterial adherence to uroepithelial cells

It’s action is INSIDE renal tubule cells so it doesn’t work if poor renal function

Broad spectrum BUT
Only used for simple UTIs

62
Q

Side effects of aminoglycosides?

A

(amikacin, gentamicin, streptomycin, tobramycin)

Common: nephrotoxicity and ototoxicity

Other:
Bronchospasm
Oliguria
Peripheral neuropathy 
Neuromuscular blockade (reverse with IV calcium gluconate)

Tobramycin also gives voice alteration, tinnitus and sore throat

63
Q

Name the four macrolides and how they work?

A

Azithromycin
Erythromycin
Clarithromycin

Inhibit ribosomal function of protein subunit 50s

64
Q

What do macrolides cover?

A

(Azithromycin, Erythromycin, Clarithromycin)

C jejuni
H influenza
Moraxella 
Chlamydia
Legionella
Actinomycetes 
Clostridium
Mycoplasma

PLUS
Gram positives:
Strep pneumonia
Staph saprolyticus

AND AZITHROMYCIN:
Neisseria
Shigella
Salmonella

65
Q

Side effects of macrolides?

A

(Azithromycin, Erythromycin, Clarithromycin)

GIT: increased peristalsis
C diff
Pancreatitis
Cholestatic hepatitis

Prolonged QT

Blood dyscrasia
Psych disturbances
Ototoxicity

66
Q

What are the two lincosamides and how do they work?

A

Clindamycin
Lincomycin

Inhibit protein synthesis by binding 50s subunit

INHIBITS toxin production so really good for GAS and toxic shock (alongside penicillin)

67
Q

Which aminoglycosides has a synergistic effect with amoxicillin?

A

Gentamicin

68
Q

Side effects of lincosamides?

A

(Clindamycin, Lincomycin)

C diff (HIGH RISK)
Go effects and LFT derangement
Blood dyscrasia
Polyarthralgias

69
Q

What mutation increases risk of ototoxicity in aminoglycosides?

A

Mutation in mitochondria DNA A1555g

70
Q

What extra thing does gentamicin cover compared to other aminoglycosides?

A

Aeromonas

71
Q

What do tetracyclines cover?

A

(doxycycline, tetracycline and minocycline)

All gram positive streps and staph

Gram negative: c jejuni, aeromonas, H influenza, moraxella, pasturella, salmonella, yersinia

Anaerobes: acinetomyces and propiobae

Chlamydia
Mycoplasma pneumonia

72
Q

What is the only gram negative with natural resistance to tetracyclines?

A

(doxycycline, tetracycline and minocycline)

Proteus mirabilus

73
Q

When should you you avoid giving tetracyclines?

A

(doxycycline, tetracycline and minocycline)

If someone is on oral retinoids (acitretin) they increase risk of benign intracranial Hypertension

74
Q

What extra thing does amikacin cover than the other aminoglycosides?

A

Mycobacterium

Nocardia

75
Q

Side effects of tetracyclines:

A

(doxycycline, tetracycline and minocycline)

GI symptoms and reflux
Photosensitivity
Tooth discolouration 
Stomatitis
Hepatitis
Benign intracranial Hypertension
76
Q

In the body where do lincosamides (clindamycin and lincomycin) act best?

A

Really good pus penetration

Really bad CNS penetration

77
Q

What is chloramphenicol?

What does it cover?

A

Binds to 50s subunit

Covers most gram positives and negatives

PLUS
Chlamydia
Mycoplasma
Rickettsia

78
Q

Side effects of chloramphenicol?

A

(Binds to 50s subunit)

Bone marrow aplasia
Grey baby syndrome

79
Q

What is Streptogramin?

When is it used?

A

A mix of a macrolide (pristinamycin 1A) and Streptogramin A (pristinamycin 2A)

Inhibit ribosome 50s subunit

Used for VRE and vanc resistant staph aureus

80
Q

Name the three tetracyclines? How do they work?

A

Doxycycline
Tetracycline
Minocycline

REVERSIBLY bind 30s subunit to prevent peptide chain elongation

81
Q

Which oxalidinone do we use?

How does it work?

A

Linezolid

Binds PROXIMALLY on 50s subunit to prevent formation of 70s complex

82
Q

What is Tigecycline?

A

Binds to 30s ribosomal subunit with 5 times affinity than tetracyclines

Covers most gram positives PLUS VRE MRSA and LISTERIA

83
Q

Is linezolid bacteriostatic or cidal?

A

Bacteriostatic against enterococci and staph

Bacteriocidal against strep

84
Q

Benefits of Linezolid?

A

Good CSF penetration

In ICU some evidence it is SUPERIOR to vancomycin

85
Q

Side effects of daptomycin

A

(daptomycin = cyclic lipopeptides)

Myopathy and rhabdo
Hepatotoxicity
Hypotension
Eosinophilic pneumonia
C diff
86
Q

What happens in linezolid resistance?

A

Bacteria develop resistance via 23S ribosome

This usually stops when linezolid is stopped

87
Q

S/E of linezolid?

A 
REVERSIBLE myelosuppression
GIT sx and LFT derangement
Serotonin syndrome
Eosinophilia
C diff
Seizures

OTOTOXIC and NEUROTOXIC due to inhibition of mitichondrial protein synthesis

88
Q

How do polymyxins (Polymyxin B and Colistin) work?

A

Target membrane phospholipids (LPS and lipoproteins)
Bind to cell membrane and disrupt the structure to make it more permeable

Gram Pos cell walls are too thick to allow it access

89
Q

How do cyclic lipopeptides (Daptomycin) work?

A

In th presence of Ca they bind to cell membrane components to cause rapid depolarisation, K efflux and cell death

**Concentration dependent killing

Gram negatives are naturally resistant

90
Q

Do fluoroquinolones cover gram negatives?

A

(ciprofloxacin, moxifloxacin and norfloxacin)

Yes!
their best effect is against enterobacter, pseudomonas and haemophilis

BUT REMEMBER moxiflox does NOT cover pseudomonas

AND moxiflox WILL cover gram positive except staph

91
Q

When should you NOT use daptomycin?

A

Pneumonia

Daptomycin is inactivated by surfactant

92
Q

When should fluoroquinolones NOT be given?

A

(ciprofloxacin, moxifloxacin and norfloxacin)

G6PD deficiency: results in haemolytic anaemia

Myasthenia gravis: can unmask it

93
Q

Side Effects of fluoroquinolones?

A

(ciprofloxacin, moxifloxacin and norfloxacin)

Reduce seizure threshold
Tendinopathy
Interstitial nephritis
Tremor and myalgias
Peripheral neuropathy
LFT derangements
QTc prolongation
94
Q

What is the mechanism for sulfamethoxazole action?

A

Nucleotide and DNA formation require TETRAHYDROFOLATE (TH4)
Bacteria make their own TH4 using PABA (para-amino-benzoid acid)

BUT Bacteria use sulfur in preference to PABA
–> so providing sulfur inhibits TH4 production

Humans dont make TH4 so our cells are unaffected

95
Q

What is the MoA for trimethoprim?

A

TH4 becomes TH2 and so it needs to be converted back by bacteria to TH4

Bacteria convert TH2 back to TH4 with DIHYDROFOLATE REDUCTASE

Trimethoprim is a COMPETITIVE inhibitor (mimics the action of) dihydrofolate reductase

96
Q

What is the MoA of fluoroquinolomes?

What are the three we commonly use?

A

Ciprofloxacin
Moxifloxacin
Norfloxacin

They inhibit bacterial DNA synthesis by inhibiting DNA gyrase and topoisomerase IV

97
Q

Which fluoroquinolone will NOT cover pseudomonas?

but WILL cover gram positives except staph

A

Moxifloxacin

98
Q

Which are the three rifamycins we use?

How do they work?

A

Rifabutin
Rifampicin
Rifamaxin

Inhibit nucleic acid synthesis by inhibiting RNA polymerase

** RifaMaxin has very poor absorption, but acts locally in the gut

99
Q

What do rifamycins target?

A

Gram positives: ONLY Haemophilus and Pasturella

Gram negatives: ALL except enterococci and listeria

100
Q

Side effect profiles of the three rifamycins

A

Rifampicin and Rifabutin: orange secretions, hepatitis and c diff
Rifabutin: neutropenia, thrombocytopenia, anaemia and uveitis
Rifampicin: Pychosis, ataxia and confusion

101
Q

What are the two nitromidazoles we use and how do they work?

A

Metronidazole
Tinidozole

Metabolised to active metabolites that interfere with DNA synthesis

102
Q

S/E of nitromidazoles?

A

Common: GI sx, CNS effects and paraesthesia, and metallic taste

Uncommon: Furry tongue, glossitis and stomatitis

Rare: SJS, peripheral neuropathy, dark urine and seizures

103
Q

Fidaxomicin: mech and used in?

A

Bactericidal, inhibits bacterial RNA synthesis by binding to RNA polymerase

Used in SEVERE c diff

BUT ONLY ACTS IN INTESTINAL LUMEN

104
Q

Hexamine Hippurate: mech and when to avoid?

A

Hydrolysed in acidic pH to become ammonia and formaldehyde

** DONT use in diarrhoea or gout as it can PRECIPIYATE URATE CRYSTALS **

105
Q

Nitrofurantoin: side effects?

A 
GIT sx, vertigo
Hepatotoxicity
Peripheral neuropathy
Lupus like syndrome
Eosinophilia
Arthralgias

Reversible allergic pneumonitis
Chronic interstitial pulm fibrosis

106
Q

Mech for sodium fusidate?

When is it used?

A

Inhibits bacterial protein synthesis by preventing translocation of protein subunits

Used in MRSA

107
Q

What drug do you avoid with sodium fusidate?

A

Statins

Causes rhabdo!

108
Q

What is dapsone?

When is it used?

A

Antimycobacterial that blocks folic acid synthesis

Used in:

  • leprosy
  • dermatitis herpetiformis
  • 2nd line in PCP
109
Q

What is ethambutol?

How does it work?

A

Anti-mycobacterial

Inhibits incorporation of mycolic acid into mycobacterium cell wall

110
Q

Side effect of ethambutol?

When should it be avoided?

A

AVOID: gout and optic neuritis

SIDE EFFECTS:
Eye: optic neuritis (decreased acuity, colour blindness and scotoma)
Gout
Renal failure
Peripheral neuritis
111
Q

What is isoniazid?
When should you avoid it?
Side effects?

A

Antimycobacterial
Inhibits synthesis of mycolic acid

**AVOID in liver disease and epilepsy

Peripheral neuropathy
Peripheral neuritis (**if not given with pyridoxane)
Hepatitis and pancreatitis
Acne
Seizures and encephalopathy and psychosis
Pellagra
Haemolytic anaemia

112
Q

What drug must you give WITH isoniazid and why?

A

Pyridoxane

prevents development of peripheral neuritis

113
Q

What increases your risk of peripheral neuropathy when giving isoniazid?

A

HIV
Diabetes
Malnutrition

114
Q

Which are broad spectrum penicillin?

A

Tazocin

115
Q

If you add clavulanate to moderate spectrum penicillins (amoxycillin and ampicillin) what do you additionally cover?

A 
More gram negative coverage:
E coli
Klebsiella
Moraxella
Shigella
yersinia
Bacterioides
116
Q

What do moderate spectrum penicillins target?

A

Gram positive: streptococcus and clostridium

Gram negative: 
Neisseria
H influenxa
Salmonella
Proteus mirabilis
117
Q

Which are the moderate spectrum penicillins?

A

Amoxycillin

Ampicillin

RACP Written 2018 (167 decks)

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