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Immunology > Lecture 18 -Antimicrobrial Therapy > Flashcards

Lecture 18 -Antimicrobrial Therapy Flashcards

1
Q

What are the characteristics of ‘ideal antimicrobrial’ ?

A

Selective toxicity: drugs that kills or inhibits growth of the pathogen without harming the host Broad spectrum Long half-life (maintain therapeutic concentrations) Easy to administer Good tissue distribution Does not interfere with other drugs and non-allergenic Resistance by microorganisms not easily acquired Reasonable cost

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2
Q

What are the classification of Antibacterial agents?

A

Based on spectrum of activity Based on mode of action

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3
Q

Based on spectrum of activity

A

Broad spectrum Narrow spectrum

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4
Q

Based on mode of action

A

Bacteriostatic Bactericidal

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5
Q

What does bactericidal do?

A

Irreversibly damages/kills bacteria (e.g. penicillins)

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6
Q

What does Bacteriostatic do?

A

Inhibit growth and multiplication of bacteria (e.g. sulphonamides)

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7
Q

What are examples of Bacteriostatic?

A

Chloramphenicol Tetracyclines Macrolides Trimethoprim Clindamycin

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8
Q

What are some examples of Bactericidal?

A

Penicillin Cephalosporins Fluoroquinolones (Ciprofloxacin) Glycopeptides (Vancomycin) Monobactams

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9
Q

In the clinic most antibacterials are better described as both Bacteriostatic and Bactericidal based on what?

A

Dose Duration of exposure The state of the invading bacteria

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10
Q

What is broad spectrum?

A

Target both gram positive or gram negative bacteria

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11
Q

What are examples of Broad spectrum?

A

Tetracycline Chloramphenicols. Fluoroquinolones Third and fourth generation cephalosporins

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12
Q

What is Narrow spectrum?

A

Only targets with gram positive or gram negative bacteria and target either Aerobes or Anaerobes

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13
Q

Polymixins

A

Only target gram negative bacteria and have Narrow spectrum

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14
Q

Glycopeptides/Bacitracin

A

Only target gram positive bacteria

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15
Q

What can detect Aerobes and targets gram positive and gram negative bacteria?

A

Aminoglycosides Sulfonamide Penicillin Actinomycin

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16
Q

What can be used clinically?

A

Antimicrobial compounds that exhibit selective toxicity

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17
Q

What is TD50?

A

Dose of drug that results in a toxic response in 50% of population

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18
Q

What is ED50?

A

Dose of drug which is therapeutically effective in 50% of the population

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19
Q

What is therapeutic index ?

A

TD50/ED50 - the higher the ratio, the efficient the toxicity of the drug will be

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20
Q

What can stop an infection?

A

Aminoglycosides

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21
Q

What does a high therapeutic index mean?

A

There is a large safety margin between beneficial and toxic doses

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22
Q

What has a low therapeutic index?

A

Aminoglycosides

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23
Q

What has a high therapeutic index?

A

Penicillins

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24
Q

What does bacteria synthesise?

A

Essential vitamins

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25
Q

What ribosomes does bacteria have ?

A

70S ribosomes (50 + 30S). Problem: mitochondria have 70S ribosomes

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26
Q

How does antibiotic selective toxicity occur?

A

Differences in structure and biosynthetic pathways between bacteria and human cells

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27
Q

What are the action of antimicrobial drugs?

A
  1. Inhibition of cell wall synthesis 2. Inhibition of protein synthesis 3. Inhibition of nucleic acid replication and transcription 4. Injury to plasma membrane 5. Inhibition of synthesis of essential metabolites
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28
Q

What are some example of inhibition of cell wall synthesis?

A

Penicillin cephalosporins Bacitracin Vancomycin

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29
Q

What is example of inhibition of protein synthesis?

A

Chloramphenicol Erythromycin Tetracyclines Streptomycin

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30
Q

What is an example of inhibition of nucleic acid replication and transcription?

A

Quinolones Rifampin

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31
Q

What is example of injury to plasma membrane?

A

Polymyxin B

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32
Q

What is an example of inhibition of synthesis of essential metabolites?

A

Sulfanilamide Trimethoprim

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33
Q

What does penicillin target?

A

Peptidoglycan and affects only growing bacteria and weakens the cell wall

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34
Q

Where are penicillin extracted from?

A

Cultures of module penicillum

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35
Q

Penicillin G

A

Narrow spectrum of activity (include strep. And staph.). Requires beta-lactam ring

36
Q

Penicillin V

A

Can be taken orally

37
Q

What are penicillin binding proteins?

A

Inactivation of transpeptidases - cross link peptidoglycan to form bacterial cell wall

38
Q

What does B-lactam antibiotics prevent cross-linking to?

A

o NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine) residues In bacterial cell wall

39
Q

What is the consequence of B-lactam antibiotics?

A

Destabilisation and osmotic rupture of bacterial cell

40
Q

What are natural penicillin susceptible to?

A

Penicillinases

41
Q

What are penicillinases?

A

B-Lactamases: cleave B-lactam ring

42
Q

What are examples of extended - spectrum penicillin?

A

Aminopenicillin (ampicillin and amoxicillin)

Carbenicillin and ticarcillin (caroxypenicillin)

43
Q

What is Augmentin a mixture of?

A 
Penicillin (e.g. amoxicillin) +
Clavulanic acid (non-competitive inhibitor of B-lactamase)
44
Q

What are Carbapenems?

A

Extremely broad-spectrum B-lactams

45
Q

What is Carbapenems resistant to?

A

B-lactamases and reserved for highly drug-resistant gram-negative pathogens

46
Q

What is Primaxin a combination of?

A

Imipenem and cilastatin

47
Q

What is primaxin active against?

A

98% of all organisms isolated in hospital

48
Q

Cephalosporin

A

Nucleus resemble those of penicillin
Inhibit cell wall synthesis in the same way as do penicillin
B-lactam rings differs slightly from that of penicillin
Widely used

49
Q

What are B-lactam antibiotics?

A

Penicillin
Cephalosporins
Monobactams
Carbapenems

50
Q

Inhibitors of protein synthesis: chloramphenicol

A

Inhibits the formation of peptide bonds in the growing polypeptide chain - bind to 50S ribosome
Has broad spectrum activity
Has serious adverse side effects (suppression of bone marrow activity)

51
Q

Inhibitors of protein synthesis: aminoglycosides

A

Bind to 30S subunit of bacterial ribosome
Interfere with initial steps of protein synthesis
Active against most gram positive and gram negative
Active against mycobacterium tuberculosis
Can cause hearing loss and kidney damage at high dose
E.g. streptomycin (1944) - Gentamicin
Aminoglycosides can change shape of 30S

52
Q

Inhibitors of protein synthesis: Tetracycline

A

Group of closely related broad-spectrum antibiotics
Produced by streptomyces spp.
Bind to 30s subunit and prevent incorporation of amino acid
Effective against gram positive and gram negative bacteria
Achieve high cellular concentration in host tissue
Effective for intracellular pathogens
Rickettsia and chlamydia

53
Q

Inhibitors of protein synthesis: macrolides

A

Presence of macrocyclic lactone ring

Inhibition of protein synthesis by binding to 50S subunit and preventing translocation of polypeptide chain on ribosome

54
Q

What are examples of macrolides?

A

Erythromycin
Azithromycin
Clarithromycin

55
Q

Chloramphenicol

A

Bind to 50s portion and inhibits formation of peptide Bond

56
Q

Erythromycin

A

Bind to 50S subunit and prevents movement along mRNA

57
Q

Tetracycline

A

Interfere with attachment of tRNA to mRNA- ribosome complex

58
Q

Aminoglycosides

A

Streptomycin
Changes shape of 30s portion
Causes code on mRNA to be read incorrectly

59
Q

Nucleic acid synthesis inhibitor: Rifampicin

A

Inhibits RNA polymerase In bacterial cells
Bind to bacterial DNA dependent RNA polymerase
Bind to beta subunit preventing transcription of RNA
Lipophilic and used for meningitis as it crosses the blood brain barrier
Not used as monotherapt as resistance can develop from a single mutation in RNA polymerase
Used in combination with other drugs to treat mycobacterium tuberculosis and some staphylococcal infections

60
Q

Quinolones

A

Nalidixic acid

61
Q

Fluoroquinolones

A

Ciprofloxacin

62
Q

What do quinolone and fluoroquinolones do?

A 
Inhibit DNA synthesis by binding to 
Topoisomerase II (DNA gyrase) prevent supercooling of circular DNA (gram negative)
Topoisomerase IV (DNA Topoisomerase) - prevent relaxation of positively supercooled DNA (gram positive e.g. Streptococcus pneumoniae)
63
Q

What are lipopeptide?

A

Antimicrobial that target fatty acid synthesis

64
Q

What attacks membrane of bacterial cell

A

Daptomycin (Cubicin)

65
Q

What is polymixin B and what is it effective for?

A

Bactericidal for gram negative bacteria

Effective for Pseudomonas aeurginosa

66
Q

What are polymixin?

A

Cationic peptides

67
Q

Colistin

A

Paediatric diarrhoea

68
Q

Polymixin B

A

Bactericidal for P.aeruginosa

69
Q

What are negatively charged?

A

LPS and PL

70
Q

What does PM compete and displace?

A

Cations (ca2+ and mg2+) from phosphate and bind to PLS (lipopolysaccharide) and PL

71
Q

What does polymixin Increase?

A

Membrane permeability

Leakage from cell

72
Q

What are examples of inhibitors for synthesis of essential metabolites?

A

Sulphonamides

Folic acid

73
Q

What is folic acid?

A

Important co-enzyme for synthesis of nucleic acids

74
Q

What does para-aminobenzoic acid (PABA) inhibit ?

A

Tetrahydrofolate

75
Q

Sulphonamides and folic acid inhibitors

A

Competitively bind with enzyme meant for PABA

Block folic acid production

76
Q

What are sulphonamides and folic acid inhibitors effective for ?

A

Treatment for UTI and burn patients

77
Q

Teixobactin

A

animal testing effective against
Clostridium difficile
Mycobacterium tuberculosis
Staphylococcus aureus

78
Q

What are the antibiotic-resistant pathogens?

A

Klebsiella
E.colj
Pseudomonas

79
Q

Mechanisms of resistance

A
  1. Blocking entry
  2. Inactivating enzymes
  3. Alteration of target molecule
  4. Effluent of antibiotic
80
Q

What do some bacterial mutants modify?

A

Porins-opening so that antibiotics are unable to enter the periplasmic space

81
Q

What does inactivating enzymes affect?

A

Natural products

Penicillin or cephalosporins

82
Q

How do you alter drugs target site?

A

Mutation

Post-translational

83
Q

Antibiotic A

A

Enters via a porin protein and reaches PBP

84
Q

Antibiotic B

A

Enters via a porin but is efficiently removed by effluent

85
Q

Antibiotics C

A

Cannot cross membrane so cannot reach target

86
Q

What are solution to AMR?

A
  1. More effective prevention in antibiotic use
  2. Targeted treatments (limit use of broad spectrum antibiotics)
  3. More informed clinical decisions
  4. Public education
87
Q

Penicillin

A

Penicillin bind to penicillin binding protein
Stimulate autolytic enzyme
Cut peptide bond
Alter structure of cell wall
Inhibit transpeptidase from cross linking
Cell wall disrupted influx of water

Immunology (20 decks)

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