CPTP 3.11 Pharmacology of Antimicrobials 2 Flashcards Preview

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Flashcards in CPTP 3.11 Pharmacology of Antimicrobials 2 Deck (21)
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1

What structure involved in protein synthesis is different in eukaryotic and prokaryotic cells, and thus can be selectively targeted by antimicrobial drugs?

Ribosomes

2

In what direction is RNA read?

5' to 3'

3

What is the first 'start' codon always used?

AUG

4

What are the three sites on a ribosome?

A, P and E:
• Activation
• Propagation
• Exit

5

Where does tRNA bind to mRNA?

At the A ('activation') site

6

Describe what happens during translation in the ribosome

• tRNA binds to mRNA at the A site of the ribosome
• The ribosome moves the mRNA along, transferring the tRNA into the P site, freeing up the A site so another tRNA molecule can match the next codon.
• The amino acids of both tRNA molecules form a peptide bond
• The confirmation of this bond breaks the bond between the tRNA in the P site and its amino acid
• This tRNA moves along to the E site and is released
• Its amino acid is still attached to the amino acid held by the subsequent tRNA molecule, which now moves across to the P site
• A site is freed up and the chain continues

7

Name the classes of antibiotics which bind to bacterial ribosomes. Name the formulary example of this drug and its route of administration. State whether each is bacteriostatic or bacteriocidal.

Tetracyclines (bacteriostatic)
• Doxycycline, oral

Aminoglycosides (bacteriocidal)
• Gentamicin, IV or IM

Macrolides (bacteriostatic)
• Clarithromycin (Oral, parenteral, IM)
• Erythromycin (Oral, parenteral)

8

What can impede oral absorption of doxycycline?

• Calcium
• Magnesium
• Aluminium salts

9

How do tetracyclines work? How is it selectively toxic?

• Bacterium pumps tetracycline into its cell

• This transport is only present in bacterial cells

• Binds to the 30s subunit of the bacterial ribosome (the bottom one)

• This inhibits the formation of the complex between the tRNA (in the 50s subunit) and the mRNA (in the 30s subunit)

10

Outline the spectrum of the tetracyclines and aminoglycosides

Tetracyclines:
• Broad spectrum

Aminoglycosides:
• Broad spectrum
• Low activity against:
> Anaerobes
> Streptococci
> Pneumococci

Macrolides:
• Narrow spectrum
• Gram negative bacteria

11

How can you tell a drug is:
1) a cephalosporin?
2) a macrolide?
3) an aminoglycoside?
4) a penicillin?
5) a sulfonamide?
6) a tetracycline?

1) begins with 'cefa-'
2) ends with '-mycin'
3) Ends with '-micin'
4) ends with '-illin'
5) begins with 'sulfa-'
6) ends with '-cycline'

12

How do aminoglycosides work?

• Irreversibly binds to the 30s subunit of the bacterial ribosome

• Causes more frequent misreading of prokaryotic genetic code

• This creates malformed protein, which is discarded

13

Which drug has high effectiveness against Haemophilus influenzae and Helicobacter pylori?

Clarithromycin

14

How do macrolides work?

REVERSIBLY binds between the A and P sites of the 50s bacterial ribosome subunit, preventing movement of the ribosome along mRNA

Causes a blocked ribosome

15

Which drug classes inhibit the enzymes used to package DNA? What is the formulary example? Is it bacteriocidal or bacteriostatic?

The quinolones (bacteriocidal)
• Ciprofloxacin

Metronidazole (Bacteriocidal)
• Metronidazole

16

How do quinolones and metronidazole work? Which of these comes in a predrug form?

• Bacteria (prokaryotes) do not have chromosomes, and instead use one DNA supercoil

• DNA gyrase is the enzyme that packages DNA into supercoils (to protect it)

• Quinolones bind the two elements (which usually spin separately to create the coiling) of DNA gyrase together

• This leaves DNA separated and prone to attack and interaction from cell contents such as lysosomes

metronidazole = predrug

17

What is the enzyme with the reverse action of DNA gyrase?

What does this do?

Bacterial Topoisomerase IV

UNWINDS DNA

18

What pathogens cause tuberculosis?

Mycobacteria

19

What is the mechanism of action of rifampicin?

Inhibits bacterial DNA-dependent RNA polymerase

20

What must be considered with rifampicin? What is it metabolised by? What is its route of administration? Is it bacteriostatic or bacteriocidal?

Reduces the effectiveness of hormonal contraceptives

The liver

Oral, bacteriocidal

21

What are the stages of TB treatment?

Initial treatment: 'RIPE' (2 months)

Rifampicin
Isoniazid
Pyrazinamide
Ethambutol

Continuation phase (4 months)