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Antimicrobials

Peptide Antibiotics
– Inhibit or compromise PGN or Outer Membrane (O.M.) – Bactericidal – Narrow Spectrum : Gram-positives or Gram –negatives – NOT absorbed from GIT (Gastrointestinal tract) – Resistance “generally” rare • Topical generally • Systemic toxicity – nephrotoxic, neurotoxic, ototoxic • Otitis externa, keratitis, dermatitis (ears, eyes, skin)
• “Last-resort” antibiotic - Vancomycin (humans primarily)
Peptide Antibiotics
• Bacitracin : inhibits peptidoglycan synthesis – Bacillus subtilis
– Topical (skin, eye, ear)
• Triple-Abx : with Polymyxin B and Neomycin – Bacitracin replaces Penicillins as topical (Staph) • Allergic contact sensitivity with Penicillins Peptide Antibiotics
• Polymyxins (Types A through E) – Damage Outer Membrane – Bacillus polymyxa
– Polymyxin B and E (called Colistin) – Gram –ves including PSA

• Topical (otitis, keratitis, dermatitis) : recall Surolan®
• Dogs/cats
• Horses - intra-uterine for Pseudomonas/Klebsiella

• Binds LPS - Endotoxin A
– Reduces LPS-reduced pyrexia at sub-MIC levels Peptide Antibiotics
• Glycopeptides: Gram-positives only – Inhibit PGN – Vancomycin largely reserved as “last-resort” drug in humans
• MRSA, Multi-drug resistant (MDR) Clostridium difficile or – E.U. ban on Avoparcin growth promoter in feed 1996 • VRE’s frequency in poultry dropped immediately • Not swine ? • Reason – Co-selection of Vancomycin/Macrolide resistance • Tylosin (Macrolide) was being used as growth promoter in feed • VRE in N.A. - arisen from hospitals Antimicrobial Drugs
• Inhibitors of Protein Synthesis
– Aminoglycosides/Aminocyclitols (ie. Streptomycin, Spectinomycin) – Lincosamides (i.e Lincomycin) – Chloramphenicol and Florfenicol Tetracyclines: Bacteriostatic
– Chlortetracycline (1944) – Oxytetracycline, Tetracycline – Semisynthetics – G+ve, G-ve, anaerobes – FIPs (Brucella, Listeria) – Obligate intracellular (Chlamydophila, – Efflux pumps – PSA, Proteus mirabilis, most – Enterobacteriaceae (E. coli, Salmonella, Klebsiella, Enterobacter) and Clostridia Tetracyclines
• Dogs/Cats - Tet, Oxytet, Doxycyline, Minocycline • Horses/Ruminants/ Swine - Oxytetracycline – Potomac Horse Fever (Neorickettsia), Leptospirosis
– Parenteral (I.V., I.M), oral (p.o.) in dogs, cats and “monogastric” food – Water/food admin – TeracyclineJ (water soluble tetracyline powder) – TerramycinJ (oxytetracycline in feed) Tetracyclines
• Dysbiosis in GIT (biliary excretion, passive diffusion into large – Predispose to enterocolitis (Salmonella, Candida, Clostridium spp. ) – Equine risk, other hindgut fermenters (Guinea pigs in particular) • Not recommended for young animals (bone, teeth) • Cardiac effects – Ca+2 binding during rapid I.V. admin Aminoglycosides(AMGs): Bactericidal
– Streptomycin/Dihydrostreptomycin
– Neomycin
– Kanamycin, Amikacin, Apramycin,
Tobramycin; Gentamicin
– Spectinomycin

Aminoglycosides: Bactericidal
• Potency/Spectrum/resistance to resistance mechanism(s) – Tobramycin>Amikacin/Gentamicin>Neomycin/Kanamycin>Streptomycin – No GIT uptake • Streptomycin/Dihydrostreptomycin: Dog, Cattle, poultry (i.m.) – Leptospirosis (with a Penicillin – this is off-label in N.A.) – Resistance has reduced use – Triple-Mix Antibiotics (skin, eye) with : Bacitracin and Polymyxin B – Otitis externa (Tresaderm®) – Oral route as well • dog/cat • Calves: oral colibacillosis – most nephrotoxic Aminoglycosides: Bactericidal
• Kanamycin (parent compound) used little due to widespread resistance • Amikacin, Gentamicin or Tobramycin are excellent options for PSA – Amikacin: Dog/Cat/Horse/Cattle (route – parenteral) – Tobramycin: ’d PSA activity (combine with ticarcillin) – Apramycin: licensed for swine (Canada, not U.S.) • enteritis (E. coli) p.o
Aminoglycosides: Bactericidal
– Gentamicin: Dog/Cat/Horse/Cattle/chicks/piglets (parenteral) or water
• Gentocin® : dog, cat, piglet (i.m.), horse ,dog, cow (intrauterine), chick (s.q.)
• 1 day old chicks, 3 day old piglets (long withdrawal time - kidney
residues)
• Gram negative sepsis (including foals, ferrets, rabbits, rodents) – I.V.
• Opthalmic spray for pinkeye (US), bacterial dermatitis in dogs (Canada)
• Spectinomycin: Narrow spectrum, little nephro- or ototoxicity but – Mycoplasma’s (poultry), colibacil osis (swine) and swine dysentery (Brachyspira) and porcine proliferative enteropathy (Lawsonia) in combination with Lincomycin (Lincosamide)

Source: http://people.upei.ca/bdespres/Antimicrobials-II-10.pdf