Antimicrobial choice

Question 1

Beta-lactams - MoA

Answer 1

–Interfere with bacterial cell wall production
→ Cell lysis

Question 2

Beta-lactams - indications/use

Answer 2

• Gram +ve bacteria
• 1st choice for streptococcal infections in horses
  –Most anaerobic infections
  –Synergistic with aminoglycosides and additive to
  fluoroquinolones
  –Limited efficacy in abscesses

Question 3

Beta-lactams - AE

Answer 3

Immune reactions

Question 4

Cephalosporins - MoA
- AE

Answer 4

–Same as penicillins but more resistant to bacterial
defences
-immune reactions

Question 5

Aminoglycosides - MoA

Answer 5

–Penetrate bacteria (Gram – pump actively into
cell)
–Bind to 30S ribosomal subunit → misreading of
genetic code
–Bactericidal
–Concentration dependant

Question 6

Aminoglycosides - use

Answer 6

Pseudomonas
Gram -ve

Question 7

Aminoglycosides - AE

Answer 7

nephrotoxicity
endotoxaemia
neuromuscular blockade
ototoxicity (ears)

Question 8

Chloramphenicol - MoA

Answer 8

–Bind to 50S ribosomal subunit → inhibit protein
synthesis
–Bacteriostatic

Question 9

chloramphenicol - use

Answer 9

broad spectrum
not for food animals
short half life IV therefore oral use

Question 10

chloramphenicol - AE

Answer 10

colitis
Not to be administered with penicillin, aminoglycosides, fluoroquinolones or macrolides
Aplastic anaemia in humans

Question 11

Potentiated sulphides - MoA

Answer 11

Inhibit folic acid pathway

Question 12

Potentiated sulphides - use

Answer 12

–Broad spectrum: Strep, Staph and some Gram –
(E.coli, Salmonella)
–Ineffective against most anaerobes
–Ineffective in pus and necrotic tissue

Question 13

Potentiated sulphonamides - AE

Answer 13

–Agranulocytosis, anaemia, thrombocytopaenia
–Crystalluria (DH)
–Diarrhoea
–Rapid i.v. Administration → collapse!
–Fatal dysrhythmias when associated with
detomidine

Question 14

Tetracyclines - MoA

Answer 14

–Binds to 30S ribosomal subunit → inhibit protein
synthesis
–Bacteriostatic
–Mammalian cells cannot transport into cell

Question 15

Tetracyclines - use

Answer 15

–Broad spectrum: gram + and -, some anaerobs,
Chlamydia, Mycoplasma, Ehrlichia, Rickettsia and
some protozoa
–Contracted tendons in foals: chelate Ca at
myotendinous junction
–Doxycycline: inhibit MMPs → keratomalacia and
IMMK

Question 16

Tetracyclines - AE

Answer 16

–Fatal colitis
–Rapid i.v. Administration → collapse + death
–Discoloration of teeth

Question 17

Fluoroquinolones - MoA

Answer 17

–Inhibit bacterial DNA gyrase → abnormal spatial
configuration of DNA
–Autolysines
–Bactericidal
–Optimal bactericidal concentration (higher or
lower → ↓ bactericidal activity

Question 18

Fluoroquinolones - use

Answer 18

–Broad spectrum: most aerobic gram -, some aerobic gram +, Mycoplasma, Chlamydia,
Rickettsia
–Very effective against enteric gram – pathogens
(Salmonella)
–Ineffective against anaerobic bacteria (beneficial
in enteric infections)

Question 19

Fluoroquinolones - AE

Answer 19

–Cartilage lesions (foals)
–Antagonistic to antimicrobials that inhibit
bacterial protein synthesis (chloramphenicol,
rifampin)
–Enrofloxacin: not in humans!

Question 20

Macrolides - MoA

Answer 20

–Binds to 50S ribosomal subunit (≈
chloramphenicol) → inhibit protein synthesis
–Bacteriostatic
–Resistance develops quickly

Question 21

Macrolides - use

Answer 21

–Associated with causing colitis in adult horses so
restricted to treatment of Rhodococcus equi in
foals
–Prokinetic (small dose i.v.)

Question 22

Macrolides - AE

Answer 22

–Diarrhoea (adults)
–Hyperthermia

Question 23

Rifampin - MoA

Answer 23

–Inhibit bacterial RNA polymerase → ↓ RNA
synthesis
–No effect on mammalian cells
–Rapid development of resistance (use in
combination)

Question 24

Rifampin - use

Answer 24

–Staph
–Rhodococcus equi
–Mycobacteria
–Some viruses and fungi

Question 25

Rifampin - AE

Answer 25

–Stains everything it contacts red
–Horses treated → red urine, faeces, tears, saliva

Question 26

Metronidazole - MoA

Answer 26

–Anaerobic bacteria take up and break into small
free radicals → DNA damage

Question 27

Metronidazole - use

Answer 27

–Anaerobic bacteria
–Protozoa (Giardia)

Question 28

Metronidazole - AE

Answer 28

–Mutagenic
–Neurotoxicity
–Depression and ↓ appetite