PHARMACOLOGY - Antimicrobials

Question 1

What is the mechanism of action of tetracyclines?

Answer 1

Tetracyclines reversibly bind to the 30S subunit of the bacterial ribosome, preventing the binding of tRNA and thus inhibiting protein synthesis

Question 2

What is the spectrum of action of tetracyclines?

Answer 2

Broad spectrum antibiotic

Question 3

How should tetracyclines be administered?

Answer 3

Intravenous (I.V)
Intramuscular (I.M)

Question 4

Why should tetracyclines not be administered orally?

Answer 4

Tetracyclines are chelating agents and would form complexes with the metal ions in food

Question 5

How are tetracyclines eliminated?

Answer 5

Tetracyclines are renally excreted and excreted in the bile

Question 6

Which mechanism increases the half life of tetracyclines?

Answer 6

Tetracyclines undergo enterohepatic recirculation (eliminated in the bile but recirculated into the gastrointestinal tract), increasing the half life of the drug

Question 7

How do tetracyclines cause severe diarrhoea in horses?

Answer 7

Tetracyclines undergo enterohepatic recirculation and can thus wipe out the normal gut microflora in horses, leading to severe diarrhoea

Question 8

What are the risks of rapid I.V. administration of tetracyclines?

Answer 8

Rapid I.V. administration of tetracyclines can lead to hypotension and sudden collapse as tetracyclines are chelating agents and will form complexes with calcium ions

Question 9

How can hypotension and sudden collapse be avoided with I.V. administration of tetracyclines?

Answer 9

This effect can be avoided via slow infusion of the drug or pretreatment I.V. calcium

Question 10

Why should tetracyclines be avoided in young animals?

Answer 10

Tetracyclines are chelating agents and will chelate with active centres of ossification

Question 11

Name two long-acting tetracyclines

Answer 11

Minocycline
Doxycycline

Question 12

Why is doxycycline used in patients with renal dysfunction?

Answer 12

Doxycycline is not renally excreted and this can be used in patients with renal dysfunction without risking further damage

Question 13

What is the mechanism of action of macrolides?

Answer 13

Macrolides reversibly bind to the 50S subunit of bacterial ribosomes, preventing the addition of new amino acids to the polypeptide chain, thus inhibiting protein synthesis

Question 14

What is spectrum of activity of macrolides?

Answer 14

Active against most Gram positive and some Gram negative bacteria

Question 15

Why are macrolides often administered orally as salts?

Answer 15

Macrolides are weak bases so would mainly exist in their ionised form due to the acidic environment in the stomach and won’t be able to cross cell membranes to enter the circulation. Through administering these drugs in the form of salts, this improves the stability of these drugs

Question 16

Why should I.M. administration of macrolides be avoided?

Answer 16

I.M. administration of macrolides can lead to injection site reactions and hypersensitivity

Question 17

What allows macrolides to be easily distributed to sites of inflammation?

Answer 17

Macrolides can enter phagocytic cells, increasing their distribution to inflammatory sites

Question 18

What is the main risk of macrolide use in horses?

Answer 18

Serious or even fatal macrolide-induced gastrointestinal disturbances

Question 19

Give an example of a macrolide drug

Answer 19

Erythromycin

Question 20

Why are aminoglycosides and fluoroquinolones used sparingly in veterinary medicine?

Answer 20

Aminoglycosides and fluoroquinolones are used sparingly as only one mutation is required for bacteria to develop antibiotic resistance to these drugs

Question 21

What is the mechanism of action for aminoglycosides?

Answer 21

Aminoglycosides bind to the A site of the 16S subunit of the 30S subunit of the bacterial ribosome, resulting in mistranslation resulting in errors in protein synthesis

Question 22

What is the spectrum of activity for aminoglycosides?

Answer 22

Narrow spectrum antibiotics

Question 23

Why are aminoglycosides narrow spectrum antibiotics?

Answer 23

Aminoglycosides require oxygen-dependent polyamine carriers to enter bacterial cells and thus can only target aerobic bacteria

Question 24

Why do aminoglycosides have such poor distribution?

Answer 24

Aminoglycosides have low lipid solubility

Question 25

(T/F) Aminoglycosides are metabolised by the liver

Answer 25

FALSE. Aminoglycosides are not metabolised

Question 26

How are aminoglycosides excreted?

Answer 26

Aminoglycosides are excreted renally

Question 27

Which antibiotic are aminoglycosides given in combination with to treat sepsis?

Answer 27

β-lactams

Question 28

What are the three toxic side effects of aminoglycosides?

Answer 28

Nephrotoxicity
Ototoxicity
Neuromuscular paralysis

Question 29

Give an example of an aminoglycoside

Answer 29

Streptomycin

Question 30

What are the two mechanisms of action of fluoroquinolones?

Answer 30

1. Fluroquinolones bind to bacterial DNA-Gyrase to form a fluoroquinolone-DNA-Gyrase ternary complex leading to bacterial cell death
2. Fluoroquinolones bind to bacterial topoisomerase enzymes to form a fluoroquinolone-topoisomerase ternary complex which inhibits the coiling of bacterial DNA

Question 31

What is the spectrum of activity for fluroquinolones?

Answer 31

Broad spectrum antibiotics

Question 32

(T/F) Fluoroquinolones have a high bioavailability

Answer 32

TRUE.

Question 33

What allows fluroquinolones to be easily distributed to sites of inflammation?

Answer 33

Fluoroquinolones can enter phagocytic cells, increasing their distribution to inflammatory sites

Question 34

How are fluoroquinolones metabolised?

Answer 34

Fluoroquinolones are metabolised by the liver

Question 35

How are fluoroquinolones excreted?

Answer 35

Fluoroquinolones are excreted in the bile and renally

Question 36

Why are fluoroquinolones contraindicated in young animals?

Answer 36

Fluoroquinolones cause erosion of articular cartilage