Antibiotic Selection

Question 1

Which antibiotics are beta-lactams?

Answer 1

Penicillin and cephalosporins

Question 2

How do beta-lactams work?

Answer 2

• Inhibit cell wall synthesis
• Bactericidal

Question 3

Spectrum of activity of beta-lactams?

Answer 3

• Many gram positive organisms
• Some gram negative organisms
• Most obligate anaerobes
  
  • Eg Strep equi var equi and zooepidemicus
• Metronidazole cannot be used in meat producing animals, have to sign them out of the food chain.

Question 4

Spectrum of activity of Penicillin G?

Answer 4

• IV form of penicillin
  
  • not licensed
• Most gram positive and gram negative cocci
• Some aerobic and anaerobic bacilli
• Not pseudomonas

Question 5

Why is Benzathine penicillin G (Pen LA) often avoided in equine practice?

Answer 5

• Slow absorption
• Fails to reach MIC
• AVOID IT
• Most licensed doses are ineffective at maintaining MIC
• datasheet doses therefore inappropriate and so often avoided

Question 6

Compare the use of penicillins between small animal and equine practice.

Answer 6

• Often first line in small animal medicine
• Requirement for IM dosing makes less popular in equine use
  
  • Effective for most respiratory and skin diseases
  • Procaine has a >4-6 week racing prohibition

Question 7

Spectrum of activity of Cephalosporins?

Answer 7

• Effective against Staph aureus
• Effective against anaerobes (except bacteroides)
  
  • Same anaerobe potential as penicillins
• Second, third and fourth generation drugs
  
  • More gram negative effects

Question 8

Which is the licensed Cephalosporin which is used in equine practice?

Answer 8

• Ceftiofur (IM) – Equine
• Only licensed one
• Effective at licensed dose
• Can use IV too

Question 9

Which small animal cephalosporin is also available (although not licensed for equids)?

Answer 9

Cephalexin (SA) – oral

Question 10

Spectrum of activity of Aminoglycosides?

Answer 10

• Bactericidal
• Spectrum of activity
  
  • Aerobic gram negative bacteria
  • Staphylococci
  • Not effective vs anaerobes (inability to pass into cell)
• Mechanims: Inhibit protein synthesis

Question 11

Toxicity of aminoglycosides?

Answer 11

• Nephrotoxic
  
  • Usually reversible but occasionally get accumulation in proximal tubule leading to cell death
• Ototoxic??? (theoretically)

Question 12

How widely used are aminoglycosides in equine practice?

Answer 12

• Widely used in equine medicine
• Usually used in combination
  
  • Gentamicin and penicillin
    
    • Go to antibiotic for a wide range of infections

Question 13

What are aminoglycosides used for in equine medicine?

Answer 13

• Used for bone and joint disease
• Surgical colic
• Extends gram negative cover when used with penicillin

Question 14

Spectrum of activity of Tetracyclines?

Answer 14

• Bacteriostatic, inhibit protein synthesis
• Spectrum of activity
  
  • Gram positive
  • Gram negative
  • Mycoplasma
  • Rickettsia and Ehrlichia (Anaplasma phagocytophila )
  • Poor anaerobic effects

Question 15

Which is the only licensed method of administration for tetracyclines in the horse?

Answer 15

• IM use leads to inflammation
• IV Use only in horses

Question 16

Toxic effects of tetracyclines?

Answer 16

• Diarrhoea – in hind gut fermenters (change in GI flora)
• Cardiac dysrrhthmias (following rapid IV administration)
• GI irritant

Question 17

Resistance to Sulphonamides / Pyrimidines?

Answer 17

• Probably most widely used in equine practice
• Widespread resistance following long term use

Question 18

Formulations available of Sulphonamides / Pyrimidines?

Answer 18

• Probably most widely used in equine practice
  
  • Powder for food, IV and paste formulations available

Question 19

Spectrum of activity of sulphonamides/pyrimidines?

Answer 19

• Bacteriostatic alone, bactericidal
• Mechanism of action
  
  • Inhibit DNA synthesis (purines)
• Spectrum of activity
  
  • Gram positive, gram negative
  • Not anaerobes

Question 20

Toxicity of TMP-S in the horse?

Answer 20

• CARDIOVASCULAR COLLPASE AND DEATH
  
  • Following IV use in the sedated horse (alpha 2)
  • Specific contraindication not to use it with an alpha 2
  • Give it very slow IV or IM
• Haemolytic anaemia
• Aplastic anaemia – rare
• NEONATAL LOSS – AVOID IN LAST TRIMESTER

Question 21

Toxicity of TMP-S in the dog?

Answer 21

• Immune mediated polyarthropathy (Doberman)
• Acute renal failure (crystalluria)

Question 22

What can TMP-S be used for?

Answer 22

• Respiratory disease
• Skin disease
• Liver disease
• Available IV and PO

Question 23

Why is TMP-S not useful for strangles?

Answer 23

Cannot use in strangles as do not work with purulent material

Question 24

Spectrum of activity of Quinolones?

Answer 24

• Broad spectrum
  
  • Mainly gram negative
    
    • Including pseudomonas
  • Poor gram positive
    
    • Not effective against streptococci (not a useful drug for treating horses with respiratory disease)
  • No anaerobic
• Mechanism of action
  
  • DNA inhibition (DNA gyrase)

Question 25

Side effects of quinolones?

Answer 25

* Damage to cartilage when used in skeletally immature animals * **Don’t use in skeletally immature animals**

Question 26

Uses of quinolones?

Answer 26

* Respiratory, skin, urinary * Gram negative disease * Exotics * Use a poultry formulation as there is no license

Question 27

Which antibiotics are protected?

Answer 27

Quinolones, 2^nd and 3^rd cephalosporins and maybe the aminoglycosides may be blocked by the EU

Question 28

How useful are Macrolides in horses?

Answer 28

* Treatment of *Rhodococcus equi* infections in foals * AVOID IN ADULT HORSES * NO VPL in veterinary species

Question 29

Side effects of macrolides?

Answer 29

* Severe diarrhoea * Effects on bacterial flora * Increased intestinal motility (Motilin receptors)

Question 30

Uses of rifampin in equids?

Answer 30

* Used in combination with macrolides for the treatment of R equi * Must be used in combination

Question 31

Spectrum of activity of Metronidazole?

Answer 31

* Effective against anaerobes * Bacteroides, Clostridium spp * Rarely used on its own * Used for mixed infections where anaerobes expected * GI disease (Helicobacter), wounds, dental

Question 32

Side effects of metronidazole?

Answer 32

* Nausea, anorexia (2%) * Causes them to go off their food

Question 33

What must you ensure if giving a horse metronidazole?

Answer 33

* Cannot be given to horses entering human food chain * Therefore any horse receiving metronidazole must be permanently declared as not being suitable for human consumption * Clients responsibility to do this * You responsibility to inform them