Species: Dogs & Cats4 dose protocols5 dosage forms
This page is a calculation and educational reference for veterinarians and veterinary students. It does not replace examination, culture and susceptibility testing, clinical judgment, or the attending veterinarian's final decision.
General dose (once daily): dog 15–30 mg/kg · cat 10–15 mg/kg · parenteralSource: Papich 2002 / Plumb's
Spectrum of activity
A bactericidal, concentration-dependent aminoglycoside (30S ribosome inhibitor); its strength is aerobic Gram-negative bacilli — Enterobacteriaceae (E. coli, Klebsiella, Proteus, Enterobacter, Serratia, Salmonella) and above all Pseudomonas aeruginosa (including many gentamicin-resistant strains). It is active against staphylococci (aerobic Gram-positive cocci) as well as Nocardia and Mycoplasma. But it is weak/unreliable against streptococci and enterococci alone (it gives synergy with a beta-lactam), and has no activity against anaerobes, fungi or viruses. Its activity drops sharply in an acidic/anaerobic environment and inside abscesses (better in an alkaline environment), and it penetrates the CNS and eye poorly. Systemic use is injectable only (not absorbed orally).
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Veterinary uses and doses
Serious Gram-negative infection
DogSource: Papich 2002 / Plumb's
Susceptible Gram-negative infection: 15–30 mg/kg · once daily · IV/IM/SC
Clinical note: Aminoglycosides are now given once daily in most patients (higher peak = better bacterial kill and post-antibiotic effect; lower trough = less renal accumulation and toxicity). Neutropenic/immunosuppressed patients may sometimes need a divided every-8-hour dose. Keep the course short (preferably ≤7 days), keep the animal fully hydrated, and monitor renal function and urinalysis (casts in urine = an early sign of nephrotoxicity). Because it concentrates in urine, it is also a reserve option for multidrug-resistant (MDR) Gram-negative UTI (ISCAID).
Clinical note: Cats are more sensitive to aminoglycoside toxicity (especially vestibular/balance); keep the dose in the 10–15 range and give once daily. Keep the course short, keep the animal hydrated, and monitor kidney and urine. In neutropenia, every-8-hour dosing is sometimes needed.
Sepsis / bacteremia
DogSource: Hardie 2000
Sepsis/bacteremia: 20 mg/kg IV · once daily
Combination therapy: with a beta-lactam (penicillin or cephalosporin) for Gram-positive/anaerobic cover and synergy
Clinical note: Do not mix the aminoglycoside and beta-lactam in one syringe/line (the aminoglycoside is inactivated); inject them separately. IV must be diluted and infused over at least 30 minutes. Use with great caution and renal monitoring in shock/dehydration and renal failure.
CatSource: Hardie 2000
Sepsis/bacteremia (cat): 15–20 mg/kg IV · once daily
Combination therapy: with a beta-lactam (penicillin or cephalosporin) for Gram-positive/anaerobic cover and synergy
Clinical note: The sepsis source gives 20 mg/kg, but because cats are more sensitive to toxicity, start at the low end (15) and go higher only with serum-level monitoring (TDM) if possible. Do not mix the aminoglycoside and beta-lactam in one line; IV diluted and over ≥30 minutes. Great caution in dehydration/renal failure.
Dosage forms
Ampoule 500 mg/2 mL
Ampoule 100 mg/2 mL
Vial 1000 mg/4 mL
Ampoule 200 mg/4 mL
Veterinary vial 50 mg/mL × 50 mL
Safety and clinical notes
⚠️ Two main toxicities: nephrotoxicity (tubular necrosis, usually reversible after stopping) and ototoxicity (8th-nerve damage — auditory and/or vestibular, which can be permanent); neuromuscular blockade can also occur.
Toxicity risk factors: pre-existing renal disease, very young (neonatal) or geriatric age, fever, sepsis and dehydration. Before starting, hydrate the animal and assess renal function.
Cats are more sensitive to the toxic effects (especially vestibular/balance); use with more caution and a more conservative dose.
For systemic use, once-daily dosing is preferred over divided dosing: both better efficacy (concentration-dependent kill + post-antibiotic effect) and less renal toxicity. Exception: a neutropenic patient may need more frequent (every-8-hour) dosing.
Monitor serum levels (TDM) for systemic use: the peak should be at least 40 µg/mL and the 4-hour sample less than 10 µg/mL. Monitor urine for casts (an early sign of kidney injury).
Only injectable use is effective (no systemic oral absorption). For IV, dilute in normal saline, 5% dextrose or Ringer's and infuse over at least 30 minutes; IM and SC absorption is good.
No activity against anaerobes, fungi or viruses, and its activity drops in abscesses/acidic/low-oxygen environments; drain abscesses. Poor CNS and ocular penetration.
Not reliable against streptococci and enterococci alone; for those it gives synergy with a beta-lactam. Do not mix the aminoglycoside and beta-lactam in one syringe/line (the aminoglycoside is inactivated).
Interactions: loop diuretics (furosemide) or osmotic diuretics (mannitol) and other nephrotoxic drugs (amphotericin B, vancomycin, cisplatin, polymyxin) increase toxicity risk; general anesthesia and neuromuscular blockers potentiate neuromuscular blockade (special caution in myasthenia gravis).
Pregnancy class C (crosses the placenta; risk of fetal 8th-nerve or kidney damage); use only in serious infection and after weighing benefit vs risk. Use with caution/avoid in working dogs (deafness risk) and in rabbits and rodents.
