Antibiotic Selection Flashcards
Which antibiotics are beta-lactams?
Penicillin and cephalosporins
How do beta-lactams work?
- Inhibit cell wall synthesis
- Bactericidal
Spectrum of activity of beta-lactams?
- 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.
Spectrum of activity of Penicillin G?
- IV form of penicillin
- not licensed
- Most gram positive and gram negative cocci
- Some aerobic and anaerobic bacilli
- Not pseudomonas
Why is Benzathine penicillin G (Pen LA) often avoided in equine practice?
- Slow absorption
- Fails to reach MIC
- AVOID IT
- Most licensed doses are ineffective at maintaining MIC
- datasheet doses therefore inappropriate and so often avoided
Compare the use of penicillins between small animal and equine practice.
- 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
Spectrum of activity of Cephalosporins?
- Effective against Staph aureus
- Effective against anaerobes (except bacteroides)
- Same anaerobe potential as penicillins
- Second, third and fourth generation drugs
- More gram negative effects
Which is the licensed Cephalosporin which is used in equine practice?
- Ceftiofur (IM) – Equine
- Only licensed one
- Effective at licensed dose
- Can use IV too
Which small animal cephalosporin is also available (although not licensed for equids)?
Cephalexin (SA) – oral
Spectrum of activity of Aminoglycosides?
- Bactericidal
- Spectrum of activity
- Aerobic gram negative bacteria
- Staphylococci
- Not effective vs anaerobes (inability to pass into cell)
- Mechanims: Inhibit protein synthesis
Toxicity of aminoglycosides?
- Nephrotoxic
- Usually reversible but occasionally get accumulation in proximal tubule leading to cell death
- Ototoxic??? (theoretically)
How widely used are aminoglycosides in equine practice?
- Widely used in equine medicine
- Usually used in combination
- Gentamicin and penicillin
- Go to antibiotic for a wide range of infections
- Gentamicin and penicillin
What are aminoglycosides used for in equine medicine?
- Used for bone and joint disease
- Surgical colic
- Extends gram negative cover when used with penicillin
Spectrum of activity of Tetracyclines?
- Bacteriostatic, inhibit protein synthesis
- Spectrum of activity
- Gram positive
- Gram negative
- Mycoplasma
- Rickettsia and Ehrlichia (Anaplasma phagocytophila )
- Poor anaerobic effects
Which is the only licensed method of administration for tetracyclines in the horse?
- IM use leads to inflammation
- IV Use only in horses
Toxic effects of tetracyclines?
- Diarrhoea – in hind gut fermenters (change in GI flora)
- Cardiac dysrrhthmias (following rapid IV administration)
- GI irritant
Resistance to Sulphonamides / Pyrimidines?
- Probably most widely used in equine practice
- Widespread resistance following long term use
Formulations available of Sulphonamides / Pyrimidines?
- Probably most widely used in equine practice
- Powder for food, IV and paste formulations available
Spectrum of activity of sulphonamides/pyrimidines?
- Bacteriostatic alone, bactericidal
- Mechanism of action
- Inhibit DNA synthesis (purines)
- Spectrum of activity
- Gram positive, gram negative
- Not anaerobes
Toxicity of TMP-S in the horse?
- 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
Toxicity of TMP-S in the dog?
- Immune mediated polyarthropathy (Doberman)
- Acute renal failure (crystalluria)
What can TMP-S be used for?
- Respiratory disease
- Skin disease
- Liver disease
- Available IV and PO
Why is TMP-S not useful for strangles?
Cannot use in strangles as do not work with purulent material
Spectrum of activity of Quinolones?
- 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
- Mainly gram negative
- Mechanism of action
- DNA inhibition (DNA gyrase)
