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antibiotics (Fach) / Aminoglycosides (Lektion)
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- Structure amino-groups with glycoside-bindings -> more amino-groups -> higher toxicity -> Spectinomycin = aminocyclitol -> no amino-sugars or glycoside-bindings -> safest
- Mechanism & Mode of action Mechanism: - 30S ribosomal subunit binding -> mistranslation -> dysfunctional protein products - cell membrane toxicity -> causes damaged electron transport -> reactive oxygen will be formed -> lipid peroxidation = RNA-damage Mode: - bactericidal - concentration-dependent (exc.: Spectinomycin is bacteriostatic) - PAE
- Spectrum Staphylococcus Gram- aerobic bacteria: - fastidious -> respiratory infecitions - Bordetella -> cennel cough, atopic rhinitis - Enterobacteriaceae -> GIT infections, UTI, mastitis, prostatitis - Proteus - Leptospira Important: - Mycoplasma: Spectinomycin - Mycobacterium: Streptomycin - Pseudomonas: Amikacin, Gentamycin, Tobramycin
- active substances 1. streptomycin 2. spectinomycin 3. gentamycin 4. amikacin 5. apramycin 6. neomycin 7. kanamycin 8. tobramycin
- Resistance ab ovo: anaerobic + Streptococcus E. coli: via plasmids -> altering enzymes (Acetylation, Adenylation) -> prevents positive charge -> no passage of inner membrane because no penetration without positive charge one-way resistance: not every aminoglycoside is equally sensitive to enzymes streptomycin < neomycin < gentamycin < tobramycin < amikacin (if streptmycin-resistance, try neomycin...)
- Gentamycin dose dog, cat: IV, IM, SC 5-10 mg/kg SID swine: PO 5 mg/kg horse: IV, IM 6.6 mg/kg SID (not authorized)
- Amikacin dose dog: IV, IM, SC 15-30 mg/kg SID cat: IV, IM, SC 10-15 mg/kg SID horse: IV, IM 10 mg/kg SID (not authorized)
- Administration, Absorption bad oral absorption -> made use of in GIT infections (careful in damaged mucous membranes and abscesses -> toxicosis) good parenteral absorption (intramammary, intrauterine, IM)
- distribution parenteral: poor -> no penetration of special barriers -> accumulatin in kidney cortex -> WP very long PO: WP no problem, because no accumulation
- metabolism liver metabolism unsignificant -> good for liver-failure patients elimination takes significantyl longer due to accumulation
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- excretion via urine in active form
- side effects one of the most toxic antibiotic group Neomycin > Gentamycin > Streptomycin > Amikacin > Spectinomycin Accumulation: amino-groups are protonate easily = positively charged, cells in ears and kidney tubules are negatively charged -> accumulation in those tissues -> nephrotoxic: always hydration, contraindicated in dehydration and careful in operation -> ototoxic: gentamycin affects hearing, neomycin affects balancing, tobramycin affects both Pinocytosis in the cell: oxidative stress -> leads to lysosomal destruction of the membranes -> leads to mitochondria damage -> apoptosis neuromuscular blockage: inhibition of ACh-release -> give very slow IV injection -> never combine with muscle relaxants -> danger of suffocation -> contraindicated in myasthenia gravis species-dependent toxicity: cats and reptiles very sensitive, always use half dose application to avoid toxicity: - SID in huge dose + make use of PAE - for long-term treatment only spectinomycin and amikacin
- Indications Mastitis Dermatitis: topical as cream Respiratory infections GIT infections otitis: ear drops (always check for intact tympanic membrane due to ototoxicity) UTI leptospirosis septicaemia