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Chemotherapy BMSC2210 > Antibacterial chemotherapy > Flashcards

Antibacterial chemotherapy Flashcards

1
Q

What are the common characteristics of antibacterials that target protein synthesis?

A

Natural products

Most target the ribosome directly and are bacteriostatic

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2
Q

What is the basis for selective toxicity in antibacterials that target protein synthesis?

A

Drugs can discriminate between the subtle structural differences between the bacterial and mammalian ribosomes - inhibit mitochondrial protein synthesis

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3
Q

What does bacteriostatic mean?

A

Agent prevents bacterial growth

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4
Q

What does bactericidal mean?

A

Agent kills the bacteria

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5
Q

What is the target for Mupirocin?

A

Isoleucyl tRNA synthetase (does not go near the ribosome)

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6
Q

Mupirocin - bactericidal or bacteriostatic?

A

Bacteriostatic

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7
Q

What is the mode of action for Mupirocin?

A

Acts as substrate analogue, binds isoleucyl tRNA synthetase and competitively inhibits the binding of isoleucine so protein synthesis can’t occur

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8
Q

Does Mupirocin treat Gram +ve or Gram -ve bacteria and why?

A

Gram +ve, because outer membrane of Gram -ve bacteria restricts access of Mupirocin

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9
Q

What is the clinical use of Mupirocin?

A

Topical ointment for staph and strep skin infections and eliminates nasal carriage MRSA

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10
Q

Why is Mupirocin not treated systemically?

A

Because it is rapidly de-esterified in the kidney and liver

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11
Q

What are the adverse effects of Mupirocin?

A

Generally well tolerated

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12
Q

What is the target for the Oxazolidinones?

A

Binding site on 50S (larger) ribosomal subunit

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13
Q

Oxazolidinones - bactericidal or bacteriostatic?

A

Bacteriostatic

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14
Q

Do oxazolidinones treat Gram +ve or Gram -ve bacteria and why?

A

Gram +ve, because the drug is removed by efflux in Gram -ve

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15
Q

What is the mode of action of the oxazolidinones?

A

Interferes with binding/correct positioning of initiator tRNA in ribosomal P site

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16
Q

What is the clinical use of the oxazolidinones?

A

IV and oral agents to treat community and hospital acquired pneumonia and skin/soft tissue infections

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17
Q

What are the adverse effects of oxazolidinones?

A

Skin reactions
Gastrointestinal disturbances
Mild and transient abnormalities in liver function
Reversible thrombocytopenia (decreased blood platelet level)
Anaemia

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18
Q

What is the target for the Tetracyclines?

A

The A site within the 30S ribosome

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19
Q

What is the mode of action of the tetracylines?

A

Bind the A site in the 30S subunit preventing association of aminoacyl-tRNA with the ribosome, preventing amino acid delivery (bacteriostatic)

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20
Q

Do tetracyclines treat Gram +ve or Gram -ve bacteria?

A

Both - they are broad spectrum

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21
Q

What is the clinical use of the Tetracyclines?

A

Mostly oral (tigecycline is IV too) used to treat skin, soft tissue and intra-abdominal infections

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22
Q

What ate the adverse effects of tetracyclines?

A

Gastrointestinal disturbances for oral products
Photosensitivity – UV sensitive – sunburn
CNS effects (particularly minocycline) - reversible
Deposition in developing bones & teeth (contraindicated in pregnancy and young children as can lead to discolouration and hyperplasia)

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23
Q

What is the target for aminoglycosides?

A

30S subunit via 16S rRNA (some bind both 30S and 50S subunits)

24
Q

Aminoglycosides - bactericidal or bacteriostatic?

A

Bactericidal (kill bacteria) unlike others

25
Q

What is the mode of action of the aminoglycosides?

A

Bind 30S subunit which reduces translational fidelity of the ribosome (increase error rate)
Abnormal proteins are produced containing external hydrophobic patches
The proteins escape the aqueous environment by folding into the membrane
The membrane integrity is compromised leading to leakage of cell contents and cell death

26
Q

What is the clinical use of the aminoglycosides?

A

Mostly IM/IV
Used alone for:
Severe sepsis by Enterobacteriaceae and Ps. Aeruginosa
Plague and tularaemia
Enterococcal endocarditis
Used in combination for:
Gram +ve and anaerobic infections and tuberculosis

27
Q

Are aminoglycosides used to treat Gram +ve or Gram -ve?

A

Both - broad spectrum

28
Q

What are the adverse effects of aminoglycosides?

A

Mechanism based toxicity:
Ototoxicity
Nephrotoxicity
Neuromuscular blockade

29
Q

What is the target for Chloramphenicol?

A

50S subunit at site overlapping the amino-acyl moiety of A site tRNA (PTC)

30
Q

What is the mode of action of Chloramphenicol?

A

Blocks amino-acyl tRNA binding - inhibiting protein synthesis

31
Q

What is the clinical use of Chloramphenicol?

A

Oral or topical
Truly broad spectrum
toxicity restricts clinical use but still used to treat typhoid and paratyphoid fever caused by Salmonella spp.

32
Q

What are the adverse effects of Chloramphenicol?

A 
Myelosuppression potentially leading to aplastic anaemia
Gray syndrome (immature excretion mechanisms)
33
Q

What is the target for the Macrolides?

A

The 23S rRNA at the peptide exit of the 50S subunit

34
Q

What is the mode of action of the Macrolides?

A

Bind the 23S rRNA at the peptide exit of the 50S subunit blocking the exit of growing peptides causing premature dissociation of the peptidyl-tRNA from the P site

35
Q

What is the clinical use of Macrolides?

A 
Oral and IV
Chlamydial infections
Mycoplasmal pneumonia
Syphilis
Corynebacterium diphtheria
Legionnaire's disease
36
Q

What are the adverse side effects of Macrolides?

A

Generally well tolerated
Some gastrointestinal disturbances
Jaundice
Ototoxicity

37
Q

What is the target for Fusidic acid?

A

Ribosome accessory factor

38
Q

What is the mode of action of fusidic acid?

A

Binds accessory factor and interferes with release of elongation factor G from the ribosome

39
Q

Does fusidic acid treat Gram +ve or Gram -ve

A

Only Gram +ve

40
Q

What are the clinical uses of Fusidic acid?

A

Topical, oral and IV therapy of staph infections

41
Q

What are the adverse effects of Fusidic acid?

A

Rashes
Jaundice
(Relatively rare)

42
Q

What are the two mechanisms by which antibacterials can target membranes?

A

Cytoplasmic membrane integrity

Cell wall synthesis

43
Q

Which two antibacterial classes target cell wall biosynthesis?

A

B-lactams and Glycopeptides

44
Q

What is the target for B-lactams?

A

Transpeptidation (cross linking between glycan strands) - structural analogues not competitive inhibitors

45
Q

What is the mode of action of the B-lactams?

A

Don’t act as a competitive inhibitor but fool the enzyme into thinking that the correct substrate is bound, prevents cross linking of peptide
Less able to resist osmotic pressure - lysis and cell death

46
Q

What are the clinical applications of B lactams?

A

Very versatile - wide and extensive use for virtually all bacterial infections (except those that lack a cell wall)

47
Q

What are the adverse effects of B lactams?

A

One of the safest antibacterials
Hypersensitivity can occur (variety of skin eruptions)
Anaphylactic shock risk after injection

48
Q

What is an issue with B lactam?

A

Showed resistance relatively early on

49
Q

What enzyme mediates B lactam resistance?

A

B lactamases

50
Q

What is the role of Clavulanic acid?

A

Lactamase inhibitor administered with B lactam to prevent resistance

51
Q

What are the four subclasses of B lactams?

A

Penicillins - “cillin”
Cephalosporins - “cef”
Carbapenems - “penem
Monobactams - “Aztreonam”

52
Q

How are cephalosporins administered?

A

IV or IM

53
Q

What are the therapeutic applications of cephalosporins?

A 
Gram +ve and -ve 
Relatively broad (especially fourth generations)
54
Q

How are the Carbapenems administered?

A

Parentally
Imipenem - IV
Meropenem - IV
Ertapenem - IV/IM

55
Q

What are the therapeutic applications of carbapenems?

A

Extremely broad but ordinarily reserved for more serious infections
Used when bacteria is resistant to penicillin and cephalosporin

56
Q

Name the main glycopeptide antibiotic

A

Vancomycin

57
Q

What is the mode of action of vancomycin?

A

Primarily affects transglycosylation (but transpeptidation also impacted)

Chemotherapy BMSC2210 (8 decks)

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