Antimicrobial choice Flashcards
Beta-lactams - MoA
–Interfere with bacterial cell wall production
→ Cell lysis
Beta-lactams - indications/use
- Gram +ve bacteria
- 1st choice for streptococcal infections in horses
–Most anaerobic infections
–Synergistic with aminoglycosides and additive to
fluoroquinolones
–Limited efficacy in abscesses
Beta-lactams - AE
Immune reactions
Cephalosporins - MoA
- AE
–Same as penicillins but more resistant to bacterial
defences
-immune reactions
Aminoglycosides - MoA
–Penetrate bacteria (Gram – pump actively into
cell)
–Bind to 30S ribosomal subunit → misreading of
genetic code
–Bactericidal
–Concentration dependant
Aminoglycosides - use
Pseudomonas
Gram -ve
Aminoglycosides - AE
nephrotoxicity
endotoxaemia
neuromuscular blockade
ototoxicity (ears)
Chloramphenicol - MoA
–Bind to 50S ribosomal subunit → inhibit protein
synthesis
–Bacteriostatic
chloramphenicol - use
broad spectrum
not for food animals
short half life IV therefore oral use
chloramphenicol - AE
colitis
Not to be administered with penicillin, aminoglycosides, fluoroquinolones or macrolides
Aplastic anaemia in humans
Potentiated sulphides - MoA
Inhibit folic acid pathway
Potentiated sulphides - use
–Broad spectrum: Strep, Staph and some Gram –
(E.coli, Salmonella)
–Ineffective against most anaerobes
–Ineffective in pus and necrotic tissue
Potentiated sulphonamides - AE
–Agranulocytosis, anaemia, thrombocytopaenia
–Crystalluria (DH)
–Diarrhoea
–Rapid i.v. Administration → collapse!
–Fatal dysrhythmias when associated with
detomidine
Tetracyclines - MoA
–Binds to 30S ribosomal subunit → inhibit protein
synthesis
–Bacteriostatic
–Mammalian cells cannot transport into cell
Tetracyclines - use
–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
Tetracyclines - AE
–Fatal colitis
–Rapid i.v. Administration → collapse + death
–Discoloration of teeth
Fluoroquinolones - MoA
–Inhibit bacterial DNA gyrase → abnormal spatial
configuration of DNA
–Autolysines
–Bactericidal
–Optimal bactericidal concentration (higher or
lower → ↓ bactericidal activity
Fluoroquinolones - use
–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)
Fluoroquinolones - AE
–Cartilage lesions (foals)
–Antagonistic to antimicrobials that inhibit
bacterial protein synthesis (chloramphenicol,
rifampin)
–Enrofloxacin: not in humans!
Macrolides - MoA
–Binds to 50S ribosomal subunit (≈
chloramphenicol) → inhibit protein synthesis
–Bacteriostatic
–Resistance develops quickly
Macrolides - use
–Associated with causing colitis in adult horses so
restricted to treatment of Rhodococcus equi in
foals
–Prokinetic (small dose i.v.)
Macrolides - AE
–Diarrhoea (adults)
–Hyperthermia
Rifampin - MoA
–Inhibit bacterial RNA polymerase → ↓ RNA
synthesis
–No effect on mammalian cells
–Rapid development of resistance (use in
combination)
Rifampin - use
–Staph
–Rhodococcus equi
–Mycobacteria
–Some viruses and fungi
Rifampin - AE
–Stains everything it contacts red
–Horses treated → red urine, faeces, tears, saliva
Metronidazole - MoA
–Anaerobic bacteria take up and break into small
free radicals → DNA damage
Metronidazole - use
–Anaerobic bacteria
–Protozoa (Giardia)
Metronidazole - AE
–Mutagenic
–Neurotoxicity
–Depression and ↓ appetite
