Lecture 19

Question 1

What is the mechanism of action of aminoglycosides?

Answer 1

The influx of bacteria causes a breakdown in protein synthesis causing a bactericidal effect

Question 2

Are the effects of aminoglycosides dose dependant or time dependant?

Answer 2

Dose dependent effects - maximize efficiency by increasing dose without changing dosing intervals

Question 3

What are the primary bacterial target of aminoglycosides?

Answer 3

Gram -ves

Question 4

Are aminoglycosides effect against anaerobes (why or why not?)?

Answer 4

Not effective against anaerobes because they enter through the cell membrane via O2-dependant transport system

Question 5

Describe the interactions between aminoglycosides and beta lactams:

Answer 5

Synergisitic other protein synthesis inhibitors (bacteriostats) are antagonistic to beta-lactams

Question 6

Why do aminoglycosides only need to be given once a day (SID)?

Answer 6

They have a long period of action (they are bactericidal after plasma concentrations decrease below MIC)

Question 7

What sites do the aminoglycosides normally accumulate in?

Answer 7

They normally selectively accumulate in vestibular and the auditory apparatus as well as in the nephrons causing nephrotoxicity and acute renal failure

Question 8

What is the main reason that aminoglycosides should be avoided in food producing species?

Answer 8

Residue concerns are the main reason why should not use these in food producing animals

Question 9

What species is gentamicin commonly used in and what species should it be avoided in?

Answer 9

Used commonly in horses and should not be used in food producing animals

Question 10

Is you wanted to treat sepsis in in a horse what combination of antibiotics could be given?

Answer 10

Gentamicin in combination with a beta-lactam to widen the spectrum of the drug

Question 11

Provide an advantage and a disadvantage of Amikacin

Answer 11

Positive: less resistance and safer than gentamicin
Negative: prohibitively expensive to systemically treat a whole horse (so better to just give it as a joint infusion)

Question 12

When is neomycin normally used?

Answer 12

It is still used in some ear and eye medications. When used systemically it has most of the side effects of the aminoglycosides

Question 13

What is (Dihydro)streptomycin normally used for?

Answer 13

Very old drug but sometimes used orally for topical GIT use in some food producing animals

Question 14

What is the function of DNA gyrase?

Answer 14

DNA gyrase - cuts the DNA up then untangles it and then rejoins it together

Question 15

What is the spectrum of activity of fluroquinolones?

Answer 15

They have greater gram -ve efficacy (mainly) than gram +ve efficacy (weak)

Question 16

What species can fluroquinolones be used in?

Answer 16

They are safe to be used against a wide range of species - people, mammals, birds, reptiles. However, they should not be used for food producing species in Australia

Question 17

Are fluroquinolones absorbed well orally?

Answer 17

Yes. Fluroquinolones have very good oral absorption.

Question 18

Do fluroquinolones distribute well?

Answer 18

They have excellent distribution - prostate, bone and skin

Question 19

What are the side effects of the fluroquinolones?

Answer 19

Quite safe. They do have mild GIT upsets, CNS stimulation at very high doses

Question 20

What is it important not to exceed enrofloxacin on label dose for cats?

Answer 20

Causes retinal degeneration. This effect is not observed with marbofloxacin and has not been assessed in other fluroquinolones

Question 21

What age group of animals should enrofloxacin be avoided in?

Answer 21

chelates magnesium leads to a loss of proteoglycan in articular cartilage (causes chondrotoxicity) - if possible avoid in young growing animals

Question 22

What is an example of a second generation fluorquinolone and what species are they mainly used in?

Answer 22

Ciprofloxacin, Marbofloxacin and Pradofloxacin (mainly used in humans)

Question 23

What is the mechanism of action of sulphonamides?

Answer 23

Bacteria must synthesis their own folate. Mammals are able to derive theirs from intestinal bacteria or preformed within the diet. Sulphonamides and Trimethoprim inhibit the synthesis and conversion of folate.

Question 24

What types of environments do sulphonamides not work well in?

Answer 24

Don’t work well in purulent environments

Question 25

Sulfonamides are bacteriostatic when used by themselves. What can be added to them to make them bactericidal?

Answer 25

When they are coupled with trimethoprim a sequential step of synergistic inhibition is created and the combination becomes bactericidal

Question 26

What is the spectrum of sulphonamides and trimethoprim?

Answer 26

Broad spectrum (Gram + and -) and coccidia (protozoa)

Question 27

Briefly describe the pharmacokinetics of sulphonamides:

Answer 27

Rapid absorption. Wide distribution (bone, CNS, joints)

Question 28

What is unique about sulfadiazine-trimethoprim?

Answer 28

It is a white liquid that can go IV (one of the two exceptions to the “nothing white goes IV” rule)