Antibiotics: Selective Toxicity & Therapeutic Index
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1
What is selective toxicity?
A drug harms microbes without significantly harming the host.
2
What does therapeutic index measure?
The safety margin between an effective dose and a toxic dose.
3
What is the therapeutic index formula?
$TI=\frac{\text{Toxic dose}}{\text{Therapeutic dose}}$
4
What does a high therapeutic index mean?
The drug has a wider safety margin.
5
What does a low therapeutic index mean?
The effective dose is closer to the toxic dose.
6
What is the therapeutic index if the toxic dose is 200 mg and the therapeutic dose is 20 mg?
10.
7
Where was penicillin originally obtained?
The fungus Penicillium.
8
Where were cephalosporins originally obtained?
The fungus Cephalosporium.
9
What are natural antibiotics?
Antibiotics produced by microorganisms.
10
What are semi-synthetic antibiotics?
Natural antibiotics chemically modified in a laboratory.
11
What are synthetic antibiotics?
Antibiotics manufactured in a laboratory.
12
What is broad-spectrum activity?
Activity against many types of bacteria.
13
What is narrow-spectrum activity?
Activity against a limited range of bacteria.
14
What does bactericidal mean?
Kills bacteria.
15
What does bacteriostatic mean?
Stops bacteria from growing and reproducing.
16
What do penicillins inhibit?
Bacterial cell-wall synthesis.
17
What structural feature do penicillins contain?
A beta-lactam ring attached to a five-sided ring.
18
How do penicillins damage bacteria?
They prevent peptidoglycan cross-linking.
19
How do cephalosporins work?
They inhibit bacterial cell-wall synthesis.
20
How do cephalosporins differ structurally from penicillins?
They have a six-sided ring attached to the beta-lactam ring.
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What are examples of cephalosporins?
Ceftriaxone and cephalexin.
22
How does bacitracin work?
It blocks transport of peptidoglycan building blocks.
23
What molecule does bacitracin interfere with?
Bactoprenol.
24
Where is bacitracin commonly used?
Topical ointments.
25
How does polymyxin B work?
It disrupts Gram-negative bacterial membranes.
26
What does polymyxin B bind to?
Lipopolysaccharide (LPS).
27
What are major polymyxin B side effects?
Kidney damage, numbness, and respiratory arrest.
28
Why is polymyxin B generally used topically?
It can be highly toxic when absorbed systemically.
29
How do quinolones and fluoroquinolones work?
They inhibit DNA gyrase and bacterial DNA replication.
30
How does rifampin work?
It inhibits bacterial RNA synthesis.
31
Which ribosomal subunit do tetracyclines bind?
The 30S subunit.
32
How do tetracyclines work?
They inhibit bacterial protein synthesis.
33
What is the spectrum of tetracyclines?
Broad-spectrum.
34
What is an important tetracycline precaution?
They can affect developing bones and teeth.
35
What do aminoglycosides do to bacterial protein synthesis?
They cause errors in protein production.
36
What are major aminoglycoside side effects?
Kidney damage and hearing loss.
37
Why must aminoglycosides be used cautiously?
They have a low therapeutic index.
38
Which ribosomal subunit do macrolides bind?
The 50S subunit.
39
How do macrolides inhibit protein synthesis?
They prevent peptide-chain elongation.
40
What structural feature do macrolides have?
A large macrocyclic lactone ring.
41
What are examples of macrolides?
Erythromycin and azithromycin.
42
What is the common name for an azithromycin treatment pack?
Z-Pak.
43
How does chloramphenicol work?
It inhibits protein synthesis at the 50S subunit.
44
What serious side effect is associated with chloramphenicol?
Aplastic anemia.
45
How do sulfonamides work?
They interfere with bacterial folic-acid synthesis.
46
Are sulfonamides natural or synthetic?
Synthetic.
47
What does isoniazid inhibit?
Mycolic-acid synthesis.
48
Which bacteria does isoniazid target?
Mycobacteria.
49
What is natural antibiotic resistance?
Resistance due to a bacterium naturally lacking the drug's target.
50
What is acquired antibiotic resistance?
Resistance gained through mutation or gene transfer.
51
How can mutations cause antibiotic resistance?
Changes in DNA can create resistance traits.
52
What is horizontal gene transfer?
Transfer of genetic material between bacteria.
53
How does antibiotic use select for resistance?
Susceptible bacteria die while resistant bacteria survive and reproduce.
54
What practices increase antibiotic resistance?
Unnecessary use and inappropriate prescribing.
55
How can antibiotic resistance be reduced?
Use antibiotics only when appropriate and follow treatment instructions.
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