Antibiotics

Question 1

Name 4 types of beta lactams.

Answer 1

(1) Penicillins
(2) Cephalosporins
(3) Carbapenem
(4) Monobactam

Question 2

What is the MOA of Beta-Lactams?

Answer 2

They inhibit cell wall synthesis. Beta lactams inhibit the transpeptidation enzyme –> this interferes with the cross-linking of the side chains of the growing peptidoglycan.

Question 3

Explain resistance to penicillins.

Answer 3

(1) Beta-lactamases destroy the beta-lactam ring.
(2) MRSA has developed an alternative penicillin binding protein, which does not allow the penicillin to bind to the bacteria.

Question 4

List 4 unwanted effects of penicillin.

Answer 4

(1) Allergic reaction: urticaria, pruritus, anaphylaxis
(2) Fever
(3) GIT disturbance: Nausea and diarrhea
(4) Rash

Question 5

What is the MOA of Vancomycin?

Answer 5

Vancomycin is a cell wall synthesis inhibitor. It inhibits the release of the building blocks of the cell wall from the lipid carrier –> they cannot be added to the growing peptidoglycan.

Question 6

How is Vancomycin administered?

Answer 6

Vancomycin is not absorbed from the GIT –> it is only given orally to treat C difficile. For other uses, it is given IV.

Question 7

What is the MOA of Bacitracin?

Answer 7

Bacitracin is a cell wall synthesis inhibitor. It interferes with the regeneration of the lipid carrier by blocking its dephosphorylation.

Question 8

List protein synthesis inhibitors.

Answer 8

(1) Tetracycline
(2) Chloramphenicol
(3) Aminoglycosides
(4) Macrolides

Question 9

What is the MOA of tetracycline?

Answer 9

Tetracycline is a protein synthesis inhibitor that works by competing with tRNA for the A site of the ribosome.

Question 10

List 4 unwanted effects of tetracycline.

Answer 10

(1) GIT disturbance: caused by direct irritation of the gut, and also by modification of the normal gut flora
(2) Staining of teeth: tetracyclines chelate calcium –> they are deposited in growing bones and teeth, which causes staining
(3) Bone deformities: also caused by chelating calcium, and being deposited in bones
(4) Increased sensitivity to sunlight

Question 11

What is the MOA of chloramphenicol?

Answer 11

Inhibits protein synthesis by interfering with the transpeptidation step - it inhibits the peptide chain on the tRNA at the P site from being transferred to the tRNA at the A site.

Question 12

What is the MOA of aminoglycosides?

Answer 12

Inhibit protein synthesis by (1) blocking the formation of the initiation complex and (2) causing misreading of the mRNA –> incorrect proteins are incorporated, and this yields a non-functioning protein.

Question 13

What are the UE of aminoglycosides?

Answer 13

(1) Ototoxic
(2) Nephrotoxic
(3) Neuromuscular blockade
(4) Allergic reactions

Question 14

What is the MOA of macrolides?

Answer 14

Protein synthesis inhibition by interfering with the translocation of tRNA from the A site to the P site.

Question 15

What 2 antibiotics inhibit cell metabolism?

Answer 15

(1) Sulfonamides

(2) Trimethoprim

Question 16

What is the MOA of sulphonamide?

Answer 16

Sulfonamide is a PABA analogue –> it competes with PABA (a precursor for folate) for the enzyme dihydropteroate synthetase.

Question 17

What is the MOA of trimethoprim?

Answer 17

Resembles folate, and interferes with dihydrofolate reductase activity.

Question 18

List 3 antibiotics that inhibit nucleic acid synthesis.

Answer 18

(1) Quinolones
(2) Metronidazole
(3) Rifampicin

Question 19

What is the MOA of quinolones?

Answer 19

Inhibit bacterial topoisomerase II –> unable to uncoil the DNA for nucleic acid synthesis

Question 20

What is the MOA of metronidazole?

Answer 20

Metronidazole has a nitroso free radical, which causes DNA damage.

Question 21

What is the MOA of rifampicin?

Answer 21

Rifampicin binds to and inhibits DNA-dependent RNA polymerase in prokaryotic cells.