Antimicrobial choice – Equine medicine

Question 1

Why are Beta-lactams commonly used?

Answer 1

Due to their safety, efficacy and low cost

Question 2

What is the mechanism of action of beta-lactams?

Answer 2

Interfere with bacterial cell wall production → Cell lysis

Question 3

Beta-lactams are the 1st choice for which infection?

Answer 3

Streptococcal infection in horses

Question 4

What are some adverse effects of beta-lactams?

Answer 4

Immune reactions: anaphylaxis (Type I hypersensitivity) , haemolytic anaemia or thrombocytopaenia (Type II)

Question 5

Describe the MOA of cephalosporins

Answer 5

Same as penicillins but more resistant to bacterial defences

• As generations increase they go more towards gram negative and have a wider spectrum of activity

Question 6

What are 2 advantages of cephalosporins?

Answer 6

• Rapid absorption following administration

- Excreted unchanged in urine (good for urinary infections)

Question 7

What is the MOA of aminoglycosides?

Answer 7

Penetrate bacteria (Gram – pump actively into cell): work within the ribosomal unit in the cell
- Bactericidal

Question 8

What are the indications of aminoglycoside use?

Answer 8

Gram –

Pseudomonas

Question 9

What are the adverse effects of aminoglycosides?

Answer 9

• Nephrotoxicity
• Endotoxaemia: ↑ death of Gram – (releasing toxins as they die)
• Ototoxicity
• Neuromuscular blockade

Question 10

What is the MOA of chloramphenicol?

Answer 10

• Bind to 50S ribosomal subunit → inhibit protein synthesis

- Bacteriostatic = suppress the growth of bacteria

Question 11

What are the indications for chloramphenicol use?

Answer 11

• Broad spectrum

- Forbidden in food production animals

Question 12

What are the adverse effects of chloramphenicol?

Answer 12

• Do not administer with penicillin, aminoglycosides, fluoroquinolones or macrolides
• Colitis
• Aplastic anaemia in humans

Question 13

Potentiated sulphonamides are ineffective in?

Answer 13

• Ineffective against most anaerobes

- Ineffective in pus and necrotic tissue

Question 14

What are the adverse effects of potentiated sulphonamides?

Answer 14

• Agranulocytosis, anaemia, thrombocytopaenia
• Crystalluria (DH)
• Diarrhoea
• Rapid i.v. Administration → collapse!

Question 15

What is the MOA of tetracyclines?

Answer 15

Binds to 30S ribosomal subunit → inhibit protein synthesis

Bacteriostatic

Question 16

What are the indications for tetracycline use?

Answer 16

• Broad spectrum: gram + and -, some anaerobes, Chlamydia, Mycoplasma, Ehrlichia, Rickettsia and some protozoa
• Contracted tendons in foals: chelate Ca at myotendinous junction

Question 17

What are the adverse effects of tetracycline?

Answer 17

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

Question 18

What is the MOA of flouroquinolones?

Answer 18

• Inhibit bacterial DNA gyrase → abnormal spatial configuration of DNA
• Autolysines
• Bactericidal

Question 19

What are the indications for fluoroquinolone use?

Answer 19

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

Question 20

What are the adverse effects of flouroquinolones?

Answer 20

• Cartilage lesions (foals): do not use in growing animals
• Antagonistic to antimicrobials that inhibit bacterial protein synthesis (chloramphenicol, rifampin)
• Enrofloxacin: not in humans

Question 21

Name 3 examples of macrolides

Answer 21

Erythromycin, clarithromycin, azithromycin (clindamycin, lincomycin)

Question 22

Describe the MOA of macrolides

Answer 22

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

Question 23

Macrolides are used to treat which disease?

Answer 23

Rhodococcus equi in foals

Question 24

Why can macrolides not be used in adult horses?

Answer 24

Cause colitis -> diarrhoea

Question 25

Describe the MOA for rifampin

Answer 25

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

Question 26

What are the indications for using rifampin?

Answer 26

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

Question 27

What are the adverse effects of rifampin?

Answer 27

• Stains everything it contacts red

- Horses treated → red urine, faeces, tears, saliva

Question 28

What is the MOA of metronidazole?

Answer 28

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

Question 29

What are the indications for using metronidazole?

Answer 29

• Anaerobic bacteria

- Protozoa (Giardia)

Question 30

What are the adverse effects of metronidazole?

Answer 30

• Mutagenic
• Neurotoxicity
• Depression and ↓ appetite

Question 31

What does the acronym PROTECT ME stand for when thinking about use of antimicrobial agents?

Answer 31

P: practice policy
R: reduce prophylaxis
O: other options
T: types of drugs and bacteria
E: employ narrow spectrum drugs
C: culture and sensitivity
T: treat effectively

M: monitor
E: educate

Question 32

What is used to treat strangles with formed abscesses?

Answer 32

Antimicrobials not indicated for abscesses

Question 33

What is the first line treatment for primary pneumonia?

Answer 33

Penicillin and gentamycin