Mechanisms of Action of Antibiotics

Question 1

What are the 3 different mechanisms antibiotics can use to inhibit or kill bacteria?

Answer 1

1. ) Inhibition of cell wall synthesis (e.g. penicillins & cephalosporins)
2. ) Inhibition of Protein synthesis (e.g. gentamicin & erythromycin)
3. ) Inhibition of nucleic acid synthesis (e.g. trimethoprim & ciprofloxacin)

Question 2

What are the 2 types of beta-lactams?

Answer 2

Penicillins and cephalosporins

Question 3

What do beta-lactams do?

Answer 3

• Disrupt peptidoglycan synthesis by inhibiting the enzymes which are responsible for cross-linking the carbohydrate chains.

INHIBIT CELL WALL SYNTHESIS

Question 4

What are the enzymes which are involved in cell wall synthesis known as?

Answer 4

Penicillin-binding proteins

PBPs

Question 5

Why are many gram negative organisms resistant to benzyl peniciliin?

Answer 5

Due to the relative impermeability of the gram negative cell wall.

Question 6

What group do penicillins and cephalosporins belong too?

Answer 6

Beta-lactams

Question 7

Why are human cells not disrupted by the action of beta-lactams?

Answer 7

They have no cell wall. Beta-lactams disrupt cell wall synthesis.

Question 8

What are the 2 groups of antibiotics that inhibit cell wall synthesis?

Answer 8

• beta-lactams

- glycopeptides

Question 9

What are the 2 glycopeptides in clincial use?

Answer 9

Vancomycin

Teicoplanin

Question 10

What do vancomycin and telcoplanin (glycopeptides) do to kill or inhibit bacteria?

Answer 10

Inhibit assembly of peptidoglycan precursor

Question 11

What type of bacteria do vancomycin and teicoplanin (glycopeptides) act on?

Answer 11

Gram positive bacteria only.

Question 12

Why are vancomycin and teicoplanin (glycopeptides) usually only given parenterally?

Answer 12

They are not absorbed in the GI tract.

Question 13

What is one of the negatives of Vancomycin use?

Answer 13

It is toxic.

Question 14

Why must iv Vancomycin be given carefully?

Answer 14

If it leaks from the veins it can cause damage to the surrounding tissue.

Must be given enough to be theraputic but not too much as to be toxic.

Question 15

What are some of the side effects of Vancomycin?

Answer 15

• Skin rash
• Ototoxicity
• Nephrotoxicity

Question 16

What is ototoxicity and nephrotoxicity?

Answer 16

ototoxicity - toxic to ears

nephrotoxicity - toxic to the kidneys.

Question 17

What are the antibiotics which are involves in the inhibition of protein synthesis?

Answer 17

• Aminoglycosides
• Macrolides & Tetracyclines
• Oxazolidinones
• Cyclic Lipopeptide

Question 18

What types of bacteria can Aminoglycosides usually work on?

Answer 18

• Gram negative bacteria
• Most staphylococci

NOT streptococci

Question 19

What is the most common aminoglycoside?

Answer 19

Gentamicin

Question 20

What is the negative of gentamicin use?

Answer 20

Gentamicin is toxic, so it requires a careful dosing regime and monitoring of levels.

Question 21

What are macrolides useful in?

Answer 21

Treatment of gram positive infections in patients that are allergic to penicillin.

Question 22

What is a negative of macrolide use?

Answer 22

A signifiant percentage of staph. aureus, strep. ptogenes and strep. pnuemoniae strains are resistant. (This must be determined through testing).

Question 23

What is the name of the common oxazolidinone?

Answer 23

Linezoid

Question 24

What is linezoid useful in?

How is it given?

Answer 24

• Treatment of MRSA / serious infections

- Orally

Question 25

What is the common cyclic lipopeptide?

Answer 25

Daptomycin

Question 26

What is daptomycin used in?

Answer 26

Treating gram positives and MRSA/ serious infections.

Question 27

What are the types of antibiotics which inhibit the synthesis of nucleic acids?

Answer 27

- Trimethoprim & sulphamethoxazole | - Fluoroquinolones

Question 28

What do trimethoprim and sulphamethoxazole do to inhibit nucleic acid synthesis?

Answer 28

Inhibit steps in purine synthesis.

Question 29

What are trimethoprim and sulphamethoxazole used in conjuction with?

Answer 29

co-trimoxazole

Question 30

Why was the use of co-trimoxazole discouraged previously but is becoming more widely used now?

Answer 30

- Discouraged due to side effects | - Increase in use because it is less likely to cause C. diff infections than other broad spectrum agents.

Question 31

What is Trimethoprim used to treat on its own?

Answer 31

UTIs

Question 32

What is a common fluroroquinolones?

Answer 32

Ciprofloxacin

Question 33

How does ciprofloxacin work? How is it taken?

Answer 33

Direct inhibition of DNA synthesis Orally and parenterally

Question 34

What is ciprofloxacin useful against?

Answer 34

Gram negative organisms

Question 35

When can ciprofloxacin not be used and why?

Answer 35

In treating children, due to the danger it could interfere with cartilage growth.