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)
Side effects of quinolones?
- Damage to cartilage when used in skeletally immature animals
- Don’t use in skeletally immature animals
Uses of quinolones?
- Respiratory, skin, urinary
- Gram negative disease
- Exotics
- Use a poultry formulation as there is no license
Which antibiotics are protected?
Quinolones, 2nd and 3rd cephalosporins and maybe the aminoglycosides may be blocked by the EU
How useful are Macrolides in horses?
- Treatment of Rhodococcus equi infections in foals
- AVOID IN ADULT HORSES
- NO VPL in veterinary species
Side effects of macrolides?
- Severe diarrhoea
- Effects on bacterial flora
- Increased intestinal motility (Motilin receptors)
Uses of rifampin in equids?
- Used in combination with macrolides for the treatment of R equi
- Must be used in combination
Spectrum of activity of Metronidazole?
- Effective against anaerobes
- Bacteroides, Clostridium spp
- Rarely used on its own
- Used for mixed infections where anaerobes expected
- GI disease (Helicobacter), wounds, dental
Side effects of metronidazole?
- Nausea, anorexia (2%)
- Causes them to go off their food
What must you ensure if giving a horse metronidazole?
- 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
