Tobramycin Sulfate

Aminoglycoside Antibiotic Antibacterial

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IM, SC, IV (slow bolus or infusion) 6-8 mg/kg/day divided q8h or q12h; or 15-20 mg/kg once daily (extended interval) q8h, q12h, or q24h Duration: Usually 5-7 days; monitor renal function
Notes: Therapeutic drug monitoring recommended; target peak 8-12 mcg/mL, trough <2 mcg/mL. Adjust dose in renal impairment.
Cat IM, SC, IV (slow bolus or infusion) 6-8 mg/kg/day divided q8h or q12h; or 15-20 mg/kg once daily (extended interval) q8h, q12h, or q24h Duration: Usually 5-7 days; monitor renal function
Notes: Cats are more sensitive to nephrotoxicity; ensure adequate hydration. Therapeutic drug monitoring recommended.
Horse (foal) IV (slow infusion) 6.6 mg/kg q24h (extended interval) or 2.2 mg/kg q8h q24h or q8h Duration: Variable; often 5-10 days
Notes: Monitor renal function and serum concentrations. For Rhodococcus equi pneumonia, combination therapy with macrolides/rifampin may be used.
Horse (adult) IV (slow infusion) 6.6 mg/kg q24h or 2.2 mg/kg q8h q24h or q8h Duration: Variable; often 5-7 days
Notes: Use with caution in dehydrated or endotoxemic horses. Monitor renal function.
Cattle IM, SC, IV (slow infusion) 5-6 mg/kg q24h (extended interval) or 2-3 mg/kg q8-12h q24h or q8-12h Duration: Usually 3-5 days
Notes: Extra-label use; observe withdrawal times. Not approved for food animals in many countries.
Small Ruminants (sheep, goats) IM, SC, IV 5-6 mg/kg q24h q24h Duration: 3-5 days
Notes: Extra-label use; observe withdrawal times.
Rabbit SC, IM, IV 2-4 mg/kg q8-12h q8-12h Duration: 5-7 days
Notes: Extra-label use; monitor renal function. May cause GI disturbances.
Bird (poultry) IM, SC 5-10 mg/kg q8-12h q8-12h Duration: 3-5 days
Notes: Extra-label use; not approved in many countries. Observe withdrawal times.
Reptiles IM 2.5-5 mg/kg q24-48h q24-48h Duration: Variable
Notes: Extra-label use; adjust based on species and temperature.

Clinical Indications & Species Uses

General Indications
  • Treatment of serious infections caused by susceptible aerobic gram-negative bacteria when less toxic antibiotics are ineffective or contraindicated
Dog (Canine)
  • Treatment of serious gram-negative bacterial infections, including Pseudomonas aeruginosa, E. coli, Klebsiella, Proteus, and Enterobacter infections
  • Septicemia
  • Pneumonia
  • Urinary tract infections (complicated)
  • Skin and wound infections
  • Otitis externa (topical)
  • Ophthalmic infections (topical)
Cat (Feline)
  • Treatment of serious gram-negative infections, including Pseudomonas, E. coli, and Klebsiella infections
  • Septicemia
  • Pneumonia
  • Urinary tract infections (complicated)
  • Skin and wound infections
  • Ophthalmic infections (topical)
Horse (Equine)
  • Treatment of gram-negative pneumonia (including Rhodococcus equi in foals)
  • Septicemia in neonates
  • Peritonitis
  • Endometritis (intrauterine infusion)
  • Ophthalmic infections (topical)
Cattle (Bovine)
  • Treatment of gram-negative infections, including pneumonia (e.g., Mannheimia haemolytica, Pasteurella multocida)
  • Septicemia
  • Metritis (intrauterine)
Small Ruminants (Sheep / Goat)
  • Treatment of gram-negative infections, including pneumonia and septicemia (extra-label use)
Rabbit & Small Mammals
  • Treatment of gram-negative infections, particularly Pasteurella multocida (respiratory infections) (extra-label use)
Avian & Poultry
  • Treatment of gram-negative infections (extra-label use; not approved in poultry in many countries)
Exotic & Other Species
  • Reptiles: Treatment of gram-negative infections (e.g., Pseudomonas, Salmonella) (extra-label use)
  • Small mammals (ferrets, guinea pigs): Treatment of gram-negative infections (extra-label use)

Pharmacology & Mechanism of Action

Drug Class: Aminoglycoside Antibiotic | Pharmacological Group: Antibacterial

Mechanism of Action: Tobramycin is a bactericidal aminoglycoside antibiotic that irreversibly binds to the 30S ribosomal subunit of susceptible bacteria, causing misreading of the genetic code and inhibition of protein synthesis. This leads to the production of nonfunctional or toxic proteins, disruption of the bacterial cell membrane, and ultimately cell death. Its action is concentration-dependent and most effective against aerobic gram-negative bacteria, particularly Pseudomonas aeruginosa.

Pharmacodynamics: Tobramycin exhibits rapid, concentration-dependent bactericidal activity. It is most effective at high peak concentrations (Cmax/MIC ratio >8-10). It has a post-antibiotic effect (PAE) against gram-negative bacilli, allowing extended dosing intervals. It is active against many Enterobacteriaceae, Pseudomonas, and some gram-positive organisms (e.g., Staphylococcus aureus), but has poor activity against anaerobes and streptococci. Resistance can occur via plasmid-mediated enzymes (acetyltransferases, phosphotransferases, adenyltransferases) or ribosomal mutations.

⚑ Pharmacokinetics Summary

Absorption: Tobramycin is poorly absorbed from the gastrointestinal tract; oral administration is ineffective for systemic infections. It is rapidly and completely absorbed after intramuscular (IM) or subcutaneous (SC) injection. Peak serum concentrations occur 30-90 minutes after IM administration. Topical application to intact skin results in minimal absorption, but absorption can occur through inflamed or denuded skin.
Distribution: Tobramycin is hydrophilic and distributes primarily into extracellular fluid. It penetrates poorly into the cerebrospinal fluid, eye (unless inflamed), and prostatic fluid. It crosses the placenta. It accumulates in the renal cortex (proximal tubular cells) and in the inner ear, which is the basis for its nephrotoxicity and ototoxicity. Volume of distribution is approximately 0.2-0.3 L/kg in most species.
Metabolism: Tobramycin undergoes minimal metabolism; it is primarily excreted unchanged by the kidneys.
Excretion: Tobramycin is eliminated almost entirely by glomerular filtration, with some tubular reabsorption. In animals with normal renal function, the elimination half-life is approximately 1-2 hours in dogs and cats, 2-3 hours in horses, and 1.5-2 hours in cattle. In neonates and animals with renal impairment, the half-life is significantly prolonged.
Half-Life: Dogs: 1-2 hours; Cats: 1-2 hours; Horses: 2-3 hours; Cattle: 1.5-2 hours; Rabbits: 1-2 hours
Bioavailability: Oral: <1% (not systemically absorbed); IM/SC: ~100%
Protein Binding: Low; approximately 10-20% bound to plasma proteins.

Available Formulations & Strengths

Injectable Solution 10 mg/mL, 40 mg/mL (vials) (IM, IV, SC, Intraperitoneal, Intrauterine, Intramammary (extemporaneous))
Ophthalmic Solution 0.3% (3 mg/mL) (Ophthalmic (topical))
Ophthalmic Ointment 0.3% (3 mg/g) (Ophthalmic (topical))
Otic Solution/Suspension 0.3% (often combined with other agents) (Otic (topical))
Powder for Oral Solution (not for systemic use) Various (for topical or oral decontamination) (Oral (not absorbed))

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to tobramycin or other aminoglycosides
  • Pre-existing severe renal impairment (unless life-threatening infection and no alternative)
  • Concurrent use of other nephrotoxic or ototoxic drugs (e.g., amphotericin B, loop diuretics, cisplatin) unless absolutely necessary
  • Myasthenia gravis (may exacerbate neuromuscular blockade)
  • Pregnancy (unless benefit outweighs risk; may cause fetal ototoxicity/nephrotoxicity)
Warnings & Clinical Precautions:
  • Nephrotoxicity: Monitor renal function (serum creatinine, BUN, urinalysis) before and during therapy, especially in patients with pre-existing renal disease, dehydration, or concurrent nephrotoxic drugs.
  • Ototoxicity: Can cause irreversible cochlear and vestibular damage; monitor for signs of hearing loss or balance disturbances.
  • Neuromuscular blockade: May cause respiratory depression or paralysis, especially in patients with neuromuscular disorders or when used with anesthetics/muscle relaxants.
  • Use with caution in neonates and geriatric animals due to immature or declining renal function.
  • Ensure adequate hydration to minimize nephrotoxicity.
  • Prolonged use may result in overgrowth of non-susceptible organisms (e.g., fungi).
  • For food animals, observe strict withdrawal times; extra-label use requires veterinary oversight.
  • Avoid contact with skin and eyes; wear gloves when handling injectable solutions.

Adverse Effects & Reactions

Common:

  • Nephrotoxicity (increased serum creatinine, BUN, proteinuria, casts)
  • Ototoxicity (vestibular and cochlear)
  • Pain at injection site
  • Gastrointestinal upset (nausea, vomiting, diarrhea) after oral administration (rare in systemic use)

Serious / Severe:

  • Acute renal failure
  • Irreversible hearing loss
  • Vestibular toxicity (ataxia, nystagmus)
  • Neuromuscular blockade leading to respiratory depression
  • Anaphylaxis (rare)

Rare:

  • Hypersensitivity reactions (skin rash, fever, eosinophilia)
  • Hematologic effects (anemia, leukopenia)
  • Electrolyte disturbances (hypokalemia, hypocalcemia, hypomagnesemia)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Loop diuretics (furosemide, ethacrynic acid) Increased risk of ototoxicity and nephrotoxicity High
Other aminoglycosides (gentamicin, amikacin) Additive nephrotoxicity and ototoxicity High
Amphotericin B Increased risk of nephrotoxicity High
Cisplatin Additive nephrotoxicity and ototoxicity High
Nonsteroidal anti-inflammatory drugs (NSAIDs) May reduce renal blood flow and increase nephrotoxicity risk Moderate
Neuromuscular blocking agents (e.g., atracurium, succinylcholine) Enhanced neuromuscular blockade, prolonged paralysis High
Inhalational anesthetics (e.g., isoflurane, sevoflurane) May enhance neuromuscular blockade Moderate
Penicillins (e.g., ticarcillin, piperacillin) In vitro inactivation of tobramycin when mixed in same solution; separate administration Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Acute renal failure (oliguria, anuria, elevated creatinine)
  • Ototoxicity (hearing loss, vestibular signs)
  • Neuromuscular blockade (muscle weakness, respiratory depression)
  • Hypocalcemia, hypomagnesemia
  • Seizures (rare)

Emergency Treatment Protocol: There is no specific antidote. Treatment is supportive and symptomatic. Discontinue tobramycin immediately. Maintain adequate hydration and urine output (consider IV fluids and diuretics if renal function is adequate). Monitor renal function, electrolytes, and acid-base status. In severe cases, hemodialysis or peritoneal dialysis may be considered to remove the drug. For neuromuscular blockade, administer calcium salts (e.g., calcium gluconate) and neostigmine (with atropine) if respiratory depression is severe. Provide respiratory support as needed.

Food Animal Withdrawal Times

πŸ₯© Meat: 30 daysπŸ₯› Milk: 7 days

Withdrawal times are not officially established for tobramycin in food animals in many countries; these are conservative estimates. Extra-label use requires veterinary oversight and extended withdrawal periods may be necessary. Consult regulatory authorities (e.g., FDA, EMA) for specific guidance.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25Β°C (68-77Β°F); avoid freezing.

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light. Keep in tightly closed container. Do not use if solution is discolored or contains particulate matter.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for human use; not FDA-approved for veterinary use in most species. However, it is available as a generic drug and used in veterinary medicine under extra-label use.

Extra-Label (Off-Label) Use: In the US, extra-label use of tobramycin in food animals is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) only with a valid veterinary-client-patient relationship, and requires extended withdrawal times. It is not approved for use in food animals in many countries. In companion animals, it is used off-label as needed.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Tobramycin is a potent aminoglycoside with excellent activity against Pseudomonas aeruginosa and other gram-negative bacteria. It is reserved for serious infections when less toxic antibiotics are ineffective. Due to its nephrotoxicity and ototoxicity, it should be used with caution, especially in animals with renal impairment or dehydration. Therapeutic drug monitoring is strongly recommended to optimize efficacy and minimize toxicity. Extended-interval dosing (once daily) is preferred in many cases to reduce toxicity while maintaining efficacy. For topical use (ophthalmic, otic), systemic absorption is minimal, but caution is advised in animals with perforated tympanic membranes. In food animals, strict adherence to withdrawal times is essential. Always consider culture and sensitivity testing before initiating therapy.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)