Equine antibiotics Flashcards
Penicillins: Mechanism of action? Bactericidal or static? Indications? When not used? Drug examples? Adverse effects?
Mechanism of action: interfere with bacterial cell wall production -> cell lysis
Bactericidal
Indications:
- G+ves
- first choice for Strep infections in horses
- most anaerobic infections
- synergistic with ahminoglycosides
Limited efficacy in abscesses (due to pH)
Poor penetration into CNS
Procaine penicillin most common in UK - IM
Adverse effects:
- anaphylaxis (type I hypersensitivity)
- haemolytic anaemia (penicillin accumulates on RBC wall)
- thrombocytopenia (type II)
- procaine penicillin: CNS signs (seizures etc) if IV or hot weather (penicillin and procaine separate if hot)
Cephalosporins: mechanism of action? Effective against? Adverse effects?
Mechanism of action: interfere with bacterial cell wall production -> cell lysis
More resistant to bacterial defences than Beta lactams
Earlier generations: mostly G+ves, very similar to penicillins
Later generations: more broad spectrum to include G-ves
Adverse effects (same as pencillins):
- anaphylaxis (type I hypersensitivity)
- haemolytic anaemia (penicillin accumulates on RBC wall)
- thrombocytopenia (type II)
Amnioglycosides: Mechanism of action? Concentration or time dependent? Cidal or static? Examples? Indications?
Mechanism of action: - penetrate bacteria (actively pumped into cell by G-ves) and bind to 30S ribosomal subunit -> misreading of genetic code - bactericidal - concentration dependent (give once at high dose and lasts long time) Examples: - gentamicin - amikacin - neomycin - streptomycin - tobramycin Indications: - G-ves - Pseudomonas - good for urinary infections but most common adverse effect is renal damage so be careful Adverse effects: - nephrotoxicity (avoid in dehydrated/renal disease or with other nephrotoxic drugs, monitor urinary GGT/creatinine, BUN, creatinine) - endotoxaemia (death of G-ves) - ototoxicity (not common) - neuromuscular blockage (not common)
Why are aminoglycosides nephrotoxic and can cause acute kidney disease?
Enters tubules after filtration
- > Uptake by cells
- > Accumulates in lysosomes
- > Lysosome rupture
- > Cell damage
Chloramphenicol: mechanism of action? Bacteriocidal or static? Indications? When not used? Adverse effects?
Mechanism of action:
- binds to 50S ribosomal subunit -> inhibits protein synsthesis
- bacteriostatic (don’t use if immunosuppressed)
Indications:
- broad spectrum
- typically only used in form of eye drops
Forbidden in food production animals
Adverse effects:
- don’t give with bactericidals
- colitis
- aplastic anaemia in humans
Potentiated sulphonamides: What are they? Mechanism of action? When not effective? Indications? Adverse effects?
Combination of sulphonamide and diaminopyrimidine
Mechanism of action:
- inhibit folic acid pathway: blocks bacterial nucleic acid synthesis
- diaminopyrimidine affects folic pathway at different step
Ineffective in pus and necrotic tissue (lots of folic acid already so bacteria doesn’t need to make its own)
Indications:
- broad spectrum: Strep, Staph, some G-ves (E.coli, Salmonella)
- good for hepatic and renal infections
Ineffective against most anaerobes
Ineffective for S equi equi
Adverse effects:
- agranulocytosis, anaemia, thrombocytopenia
- crystalluria
- diarrhoea
- rapid IV administration -> collapse!
- fatal dysrhythmias when given with detomidine
So give IV slowly and don’t give in sedated horses
Tetracyclines: Mechanism of action? Bactericidal or static? Indications? Adverse effects?
Mechanism of action:
- binds to 30S ribosomal subunit -> inhibits protein synthesis
- bacteristatic
- mammalian cells cannot transport into cell
Indications:
- broad spectrum: G+ and G-, some anaerobes, Chlamydia, Mycoplasma, Ehrlichia, Ricketssia, some protozoa
- contracted tendons in foals (chelates calcium at myotendinous junction)
- doxyxycline inhibits MMPs - keratomalacia and IMMK
- good penetration (good for abscesses, intracellular infections etc)
Adverse effects:
- fatal colitis
- rapid IV -> collapse and death
- discolouration of teeth
- doxy - oral ulceration
Fluoroquinolones: Mechanism of action? Bactericidal or static?
Mechanism of action:
- inhibit bacterial DNA gyrase -> abnormal spatial configuration of DNA
- autolysines produced by bacteria kill damaged DNA
- need optimal bactericidal concentration (if too high bacteria can’t produce autolysines)
Indications:
- broad spectrum: most aerobic G-ves, some aerobic G+ves, Mycoplasma, Chlamydia, Rickettsia
- very effective against enteric G-ves (Salmonella)
Ineffective against anaerobic bacteria (beneficial in enteric infections)
Adverse effects:
- cartilage lesions (foals)
- antagonistic to antibiotics that inhibit bacterial protein synthesis (chloramphenicol, rifampin)
Macrolides: mechanism of action? Bacteriocidal or static? Examples? Indications? Adverse effects?
Mechanism of action:
- binds to 50S ribosomal subunit -> inhibits protein synthesis
- bacteriostatic
- resistance develops quickly so always given with another drug
Examples:
- erythromycin
- claruthromycin
- azithromycin (foals only)
- clindamycin and lincomycin not used in horses
Indications:
- associated with causing colitis in adult horses so restricted to treatment of Rhodococcus equi in foals
- pro kinetic (small dose IV)
Adverse effects:
- colitis and diarrhoea in adults
- hyperthermia (be careful using in hot weather)
Rifampin: Mechanism of action? Indications? Adverse effects?
Mechanism of action: - inhibits bacterial RNA polymerase -> inhibits RNA synthesis - no effect on mammalian cells - rapid development of resistance (used with another drug) Indications: - Staph - Rhodococcus equi (main use, in combo with macrolides) - Mycobacteria - Some viruses and fungi Adverse effects: - stains everything it contacts red - red urine, faeces, tears, saliva
Metronidazole: Mechanism of action? Indications? Adverse effects?
Mechanism of action: - anaerobic bacteria take up and break into small free radicals -> DNA damage Indications: - anaerobes - protozoa (Giardia) Adverse effects: - mutagenic - neurotoxicity - depression and reduced appetite (poor palatability so can give rectally if makes horse feel worse orally)
When do wounds no longer need antibiotics usually?
Generally not needed once granulation tissue established
What does PROTECT ME stand for for antibiotic usage in horses?
Practice policy Reduce prophylaxis Other options Types of drugs and bacteria Employ narrow spectrum drugs Culture and sensitivity Treat effectively
Monitor
Educate
Which antibiotics can be given orally?
Doxycycline Trimethoprim/sulphadiazine Rifampin Azithromycin Enrofloxacin Metronidazole
Which antibiotics are first line in horses?
Procaine penicillin Sodium penicillin Oxytetracycline TMPS Gentamicin Neomycin Rifampin Azithromycin
Which antibiotics are protected in horses?
Benthazine penicillin (LA)
Ceftiofur
Cefquinome
Enrofloxacin
What first line antibiotic would be used for strangles?
Not indicated if abscessed formed
Penicillin first line for prophylaxis/airway obstruction
What first line antibiotic would be used for primary sinusitis?
Penicillin
What first line antibiotic would be used for secondary pneumonia (e.g. following RAO)?
TMPS
What first line antibiotic would be used for guttural pouch empyema/chondroids?
Penicillin
???
What first line antibiotic would be used for URT diseases which are not strangles or primary sinusitis?
TMPS
What first line antibiotic would be used for primary pneumonia?
Penicillin and gentamicin
What first line antibiotic would be used for Rhodococcus pneumonia?
Rifampin and azithromycin
What first line antibiotic would be used for contaminated wounds with synovial sepsis?
Penicillin and gentamicin
