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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
What ribosomes does bacteria have ?
70S ribosomes (50 + 30S). Problem: mitochondria have 70S ribosomes
26
How does antibiotic selective toxicity occur?
Differences in structure and biosynthetic pathways between bacteria and human cells
27
What are the action of antimicrobial drugs?
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
28
What are some example of inhibition of cell wall synthesis?
Penicillin cephalosporins Bacitracin Vancomycin
29
What is example of inhibition of protein synthesis?
Chloramphenicol Erythromycin Tetracyclines Streptomycin
30
What is an example of inhibition of nucleic acid replication and transcription?
Quinolones Rifampin
31
What is example of injury to plasma membrane?
Polymyxin B
32
What is an example of inhibition of synthesis of essential metabolites?
Sulfanilamide Trimethoprim
33
What does penicillin target?
Peptidoglycan and affects only growing bacteria and weakens the cell wall
34
Where are penicillin extracted from?
Cultures of module penicillum
35
Penicillin G
Narrow spectrum of activity (include strep. And staph.). Requires beta-lactam ring
36
Penicillin V
Can be taken orally
37
What are penicillin binding proteins?
Inactivation of transpeptidases - cross link peptidoglycan to form bacterial cell wall
38
What does B-lactam antibiotics prevent cross-linking to?
o NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine) residues In bacterial cell wall
39
What is the consequence of B-lactam antibiotics?
Destabilisation and osmotic rupture of bacterial cell
40
What are natural penicillin susceptible to?
Penicillinases
41
What are penicillinases?
B-Lactamases: cleave B-lactam ring
42
What are examples of extended - spectrum penicillin?
Aminopenicillin (ampicillin and amoxicillin) | Carbenicillin and ticarcillin (caroxypenicillin)
43
What is Augmentin a mixture of?
``` Penicillin (e.g. amoxicillin) + Clavulanic acid (non-competitive inhibitor of B-lactamase) ```
44
What are Carbapenems?
Extremely broad-spectrum B-lactams
45
What is Carbapenems resistant to?
B-lactamases and reserved for highly drug-resistant gram-negative pathogens
46
What is Primaxin a combination of?
Imipenem and cilastatin
47
What is primaxin active against?
98% of all organisms isolated in hospital
48
Cephalosporin
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
What are B-lactam antibiotics?
Penicillin Cephalosporins Monobactams Carbapenems
50
Inhibitors of protein synthesis: chloramphenicol
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
Inhibitors of protein synthesis: aminoglycosides
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
Inhibitors of protein synthesis: Tetracycline
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
Inhibitors of protein synthesis: macrolides
Presence of macrocyclic lactone ring | Inhibition of protein synthesis by binding to 50S subunit and preventing translocation of polypeptide chain on ribosome
54
What are examples of macrolides?
Erythromycin Azithromycin Clarithromycin
55
Chloramphenicol
Bind to 50s portion and inhibits formation of peptide Bond
56
Erythromycin
Bind to 50S subunit and prevents movement along mRNA
57
Tetracycline
Interfere with attachment of tRNA to mRNA- ribosome complex
58
Aminoglycosides
Streptomycin Changes shape of 30s portion Causes code on mRNA to be read incorrectly
59
Nucleic acid synthesis inhibitor: Rifampicin
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
Quinolones
Nalidixic acid
61
Fluoroquinolones
Ciprofloxacin
62
What do quinolone and fluoroquinolones do?
``` 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
What are lipopeptide?
Antimicrobial that target fatty acid synthesis
64
What attacks membrane of bacterial cell
Daptomycin (Cubicin)
65
What is polymixin B and what is it effective for?
Bactericidal for gram negative bacteria | Effective for Pseudomonas aeurginosa
66
What are polymixin?
Cationic peptides
67
Colistin
Paediatric diarrhoea
68
Polymixin B
Bactericidal for P.aeruginosa
69
What are negatively charged?
LPS and PL
70
What does PM compete and displace?
Cations (ca2+ and mg2+) from phosphate and bind to PLS (lipopolysaccharide) and PL
71
What does polymixin Increase?
Membrane permeability | Leakage from cell
72
What are examples of inhibitors for synthesis of essential metabolites?
Sulphonamides | Folic acid
73
What is folic acid?
Important co-enzyme for synthesis of nucleic acids
74
What does para-aminobenzoic acid (PABA) inhibit ?
Tetrahydrofolate
75
Sulphonamides and folic acid inhibitors
Competitively bind with enzyme meant for PABA | Block folic acid production
76
What are sulphonamides and folic acid inhibitors effective for ?
Treatment for UTI and burn patients
77
Teixobactin
animal testing effective against Clostridium difficile Mycobacterium tuberculosis Staphylococcus aureus
78
What are the antibiotic-resistant pathogens?
Klebsiella E.colj Pseudomonas
79
Mechanisms of resistance
1. Blocking entry 2. Inactivating enzymes 3. Alteration of target molecule 4. Effluent of antibiotic
80
What do some bacterial mutants modify?
Porins-opening so that antibiotics are unable to enter the periplasmic space
81
What does inactivating enzymes affect?
Natural products | Penicillin or cephalosporins
82
How do you alter drugs target site?
Mutation | Post-translational
83
Antibiotic A
Enters via a porin protein and reaches PBP
84
Antibiotic B
Enters via a porin but is efficiently removed by effluent
85
Antibiotics C
Cannot cross membrane so cannot reach target
86
What are solution to AMR?
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
Penicillin
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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