Antimicrobial choice – Equine medicine Flashcards
Why are Beta-lactams commonly used?
Due to their safety, efficacy and low cost
What is the mechanism of action of beta-lactams?
Interfere with bacterial cell wall production → Cell lysis
Beta-lactams are the 1st choice for which infection?
Streptococcal infection in horses
What are some adverse effects of beta-lactams?
Immune reactions: anaphylaxis (Type I hypersensitivity) , haemolytic anaemia or thrombocytopaenia (Type II)
Describe the MOA of cephalosporins
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
What are 2 advantages of cephalosporins?
- Rapid absorption following administration
- Excreted unchanged in urine (good for urinary infections)
What is the MOA of aminoglycosides?
Penetrate bacteria (Gram – pump actively into cell): work within the ribosomal unit in the cell - Bactericidal
What are the indications of aminoglycoside use?
Gram –
Pseudomonas
What are the adverse effects of aminoglycosides?
- Nephrotoxicity
- Endotoxaemia: ↑ death of Gram – (releasing toxins as they die)
- Ototoxicity
- Neuromuscular blockade
What is the MOA of chloramphenicol?
- Bind to 50S ribosomal subunit → inhibit protein synthesis
- Bacteriostatic = suppress the growth of bacteria
What are the indications for chloramphenicol use?
- Broad spectrum
- Forbidden in food production animals
What are the adverse effects of chloramphenicol?
- Do not administer with penicillin, aminoglycosides, fluoroquinolones or macrolides
- Colitis
- Aplastic anaemia in humans
Potentiated sulphonamides are ineffective in?
- Ineffective against most anaerobes
- Ineffective in pus and necrotic tissue
What are the adverse effects of potentiated sulphonamides?
- Agranulocytosis, anaemia, thrombocytopaenia
- Crystalluria (DH)
- Diarrhoea
- Rapid i.v. Administration → collapse!
What is the MOA of tetracyclines?
Binds to 30S ribosomal subunit → inhibit protein synthesis
Bacteriostatic
What are the indications for tetracycline use?
- Broad spectrum: gram + and -, some anaerobes, Chlamydia, Mycoplasma, Ehrlichia, Rickettsia and some protozoa
- Contracted tendons in foals: chelate Ca at myotendinous junction
What are the adverse effects of tetracycline?
- Fatal colitis
- Rapid i.v. Administration → collapse + death
- Discoloration of teeth
What is the MOA of flouroquinolones?
- Inhibit bacterial DNA gyrase → abnormal spatial configuration of DNA
- Autolysines
- Bactericidal
What are the indications for fluoroquinolone use?
- 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)
What are the adverse effects of flouroquinolones?
- Cartilage lesions (foals): do not use in growing animals
- Antagonistic to antimicrobials that inhibit bacterial protein synthesis (chloramphenicol, rifampin)
- Enrofloxacin: not in humans
Name 3 examples of macrolides
Erythromycin, clarithromycin, azithromycin (clindamycin, lincomycin)
Describe the MOA of macrolides
- Binds to 50S ribosomal subunit (≈ chloramphenicol) → inhibit protein synthesis
- Bacteriostatic
- Resistance develops quickly
Macrolides are used to treat which disease?
Rhodococcus equi in foals
Why can macrolides not be used in adult horses?
Cause colitis -> diarrhoea
Describe the MOA for rifampin
- Inhibit bacterial RNA polymerase → ↓ RNA synthesis
- No effect on mammalian cells
- Rapid development of resistance (use in combination)
What are the indications for using rifampin?
- Staph
- Rhodococcus equi
- Mycobacteria
- Some viruses and fungi
What are the adverse effects of rifampin?
- Stains everything it contacts red
- Horses treated → red urine, faeces, tears, saliva
What is the MOA of metronidazole?
Anaerobic bacteria take up and break into small free radicals → DNA damage
What are the indications for using metronidazole?
- Anaerobic bacteria
- Protozoa (Giardia)
What are the adverse effects of metronidazole?
- Mutagenic
- Neurotoxicity
- Depression and ↓ appetite
What does the acronym PROTECT ME stand for when thinking about use of antimicrobial agents?
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
What is used to treat strangles with formed abscesses?
Antimicrobials not indicated for abscesses
What is the first line treatment for primary pneumonia?
Penicillin and gentamycin
