L2_Antibiotics: A logical approach

Question 1

On what basis are antibiotics categorised into groups?

Answer 1

• by their mechanism of action.

Question 2

What is the name given to the group of antibiotics that inhibit cell wall synthesis or function?
Give 3 examples.

Answer 2

• β-lactams.
• penicillins.
• cephalosporins.
• vancomycin.

Question 3

What is the difference between bactericidal and bacteriostatic antibiotics?
Give an example of an antibiotic for each.

Answer 3

• bactericidal = kills the bacteria. e.g. (all β-lactams) penicillin.
• bacteriostatic = prevent further bacterial replication. e.g. macrolides.

Question 4

Give a brief explanation of MoA of penicillin.

Answer 4

• inhibits cell wall formation by preventing PDG cross-linkage.
• irreversibly binds to penicillin-binding proteins (transpeptidase) in the cell wall.
• these proteins are involved in the final step of PDG cross-link formation.

Question 5

Explain the role of β-lactamase in relation to penicillin.

Answer 5

• beta-lactamase hydrolyses the lactam ring in penicillin causing it to lose its structure and therefore rendering it inactive as an antibiotic.

Question 6

How can bacteria grow resistant against penicillin?

Answer 6

• many bacteria contain the gene code for β-lactamase which can be passed on to the next generation of bacteria through plasmids.

Question 7

Give one way to overcome the issue of antibiotic resistance with regards to penicillin.

Answer 7

• a combination of amoxicillin and clavulanic acid can be administered.
• clavulanic acid is a β-lactamase inhibitor.

Question 8

What feature of cephalosporins make them more stable than penicillins?

Answer 8

• they have a modified β-lactam ring which makes them less susceptible to β-lactamases.

Question 9

How is vancomycin different to penicillin? (2)

Answer 9

• it is a non-β-lactam bactericidal antibiotic.

- it is effective against anaerobic and aerobic gram-POSITIVE bacteria.

Question 10

In which instance would vancomycin be used?

Answer 10

• colitis (inflammation of the intestine).
• endocarditis.
• skin infections.
• blood stream infections.
• meningitis caused by MRSA.

Question 11

What features of vancomycin makes it suitable for treating intestinal bacterial infections?

Answer 11

• when taken orally, it is poorly absorbed from the intestines, therefore prolonging its activity within the intestines.

Question 12

What is teicoplanin and when is it typically used?

Answer 12

• an antibiotic used in prophylaxis of MRSA.
• comes in a powder which can be dissolved in water.
• cell-wall synthesis inhibitor.

Question 13

What is the therapeutic range in which vancomycin must remain in a patient? Why must the concentration not fall out of this range?

Answer 13

• 10-15 mg^L.
• below = bacteria can continue to replicate.
• above = renal toxicity.

Question 14

Which antibiotics inhibit bacterial protein synthesis? Give an example of antibiotics inhibiting the large (50s) subunit and the small (30s) subunit.

Answer 14

• large subunit = macrolides (erythromycin).

- small subunit = gentamicin

Question 15

Why is erythromycin a good antibiotic for lower and upper respiratory tract infections?

Answer 15

• due to its strong sputum and lung penetration.

Question 16

Which three drugs does erythromycin have interactions with? (3)

Answer 16

• warfarin, statins and carbomazepine.

Question 17

Briefly describe the MoA of erythromycin.

Answer 17

• it inhibits the 50s subunit of ribosomes in bacteria.

- preventing the ribosome to move along the mRNA chain and therefore preventing the production of proteins.

Question 18

Briefly describe the MoA of gentamicin.

Answer 18

• bacteriostatic against aerobic gram-NEGATIVE bacteria.
• needs oxygen for active transport (bc it is not hydrophilic) across the membrane of gram-ve bacteria.
• attaches to transfer RNA.

Question 19

Why can’t gentamicin be given orally?

Answer 19

• bc it is not lipophilic therefore has poor absorption into the systemic circulation.
• needs to given as IV.

Question 20

How does gentamicin cause ototoxicity?

Answer 20

• due to large rapid IV doses.
• causes a peak in plasma conce which leads to higher uptake in the lymph in the middle ear –> killing the hearing cells.

Question 21

Which group of antibiotics inhibit DNA synthesis?

Answer 21

• flouroquinolones = ciprofloxacin.

Question 22

Which group of antibiotics inhibit folate synthesis?

Answer 22

• trimethoprim.

Question 23

Which group of antibiotics create free radicals?

Answer 23

• metronidazol.

Question 24

What is the mechanism of action of ciprofloxacin?

Answer 24

• it blocks DNA replication.
• broad-spec antibiotic.
• bacteriostatic.
• it inhibits topoisomerase (enzyme in bacteria required to separate the DNA strands in order to initiate replication).

Question 25

Pros of ciprofloxacin:

Answer 25

• well absorbed orally.
• limited metabolism from liver so excreted mostly unchanged.
• good distribution into CNS.

Question 26

Which two drugs constitute septrim?

Answer 26

• trimethoprim and sulfamethoxazole

Question 27

What is the MoA of septrim?

Answer 27

• inhibits sequential steps in the folic acid synthesis process in bacteria.

Question 28

What is the MoA of metronidazole?

Answer 28

• effective against anaerobes.
• acts as an electron sink.
• allowing for free radicals to accumulate within the cell creating the illusion that the cell is in an oxygen rich environment.
• enters bacterial cells via passive diffusion.
• the free radicals eventually cause DNA breakage.

Question 29

Pros of metronidazole:

Answer 29

• nearly 100% bioavailability.

Question 30

Cons of metronidazole:

Answer 30

• can’t drink alcohol with it.