Gentamicin Sulfate
Gentamicin sulfate
Also known as: Gentocin · Garamycin · Amtech Gentamax 100 · Gentafuse · Gentaved · Gentozen · Legacy · Garasol · Garacin · Gen-Gard · Clinagel Vet · Easotic · Otomax · Tiacil · Genticin · gentamicin sulphate · gentamicini sulfas · NSC-82261 · Sch-9724 · Gentamicine · Gentamycin
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceSusceptible infections (extra-label)
Verified clinician required
- q24h
NA
Governing clinical context (3)
- NOTE: Most infectious disease clinicians agree that aminoglycosides should be dosed once a day in most patients (mammals) with uncompromised renal function. This dosing regimen yields higher peak levels with resultant greater bacterial kill, and as aminoglycosides exhibit a postantibiotic effect, surviving susceptible bacteria generally do not replicate as rapidly even when antibiotic concentrations are below MIC. Periods where levels are low may decrease the adaptive resistance (bacteria take up less drug in the presence of continuous exposure) that can occur. Once-daily dosing may also decrease the toxicity of aminoglycosides, as lower urinary concentrations may mean less uptake into renal tubular cells.
- ■ Therapeutic drug monitoring (TDM) when possible in patients with uncompromised renal function; highly recommended for patients with risk factors for nephrotoxicity. Peak and trough levels are determined through samples collected 30 minutes after administration (peak) and immediately before administration of the next dose (trough). Generally, peak levels (≈30 to 60 minutes post IV dose) should be greater than 32 μg/mL and trough levels less than 1 – 2 μg/mL. 34 A clinical laboratory may be able to assist in sample-time determination and dosage amount and frequency adjustment.
- Gentamicin sulfate for injection and the oral solution should be stored at room temperature (15°C-30°C [59°F-86°F]); freezing or temperatures above 40°C (104°F) should be avoided. The soluble powder should be stored from 2°C to 30°C (46°F-86°F). Do not store or offer medicated drinking water in rusty containers or the drug may be destroyed.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Gentamicin is a potent parenteral aminoglycoside antibiotic primarily used for serious gram-negative aerobic bacterial infections.
Key pharmacological features include:
- Spectrum of Activity: Excellent against gram-negative aerobes (e.g., E. coli, Klebsiella, Proteus, Pseudomonas, Salmonella) and some staphylococci. It is inactive against anaerobes, fungi, and viruses.
- Concentration-Dependent Bactericidal Activity: Efficacy is driven by achieving a high peak serum concentration relative to the Minimum Inhibitory Concentration (MIC) of the pathogen.
- Post-Antibiotic Effect (PAE): Bacterial growth remains suppressed even after drug concentrations fall below the MIC, which supports the modern practice of once-daily dosing.
- Toxicity Profile: Because of significant risks for nephrotoxicity and ototoxicity, systemic use is generally reserved for severe infections where less toxic alternatives are ineffective.
Clinical Pearl: Risk factors for toxicity include preexisting renal disease, age (neonates and geriatrics), fever, sepsis, and dehydration. Cats are particularly sensitive to the vestibular (ototoxic) effects.
Mechanism of action
Gentamicin is a concentration-dependent bactericidal antibiotic.
- Mechanism: It actively transports across the bacterial cell membrane via an oxygen-dependent mechanism → irreversibly binds to the 30S ribosomal subunit → causes misreading of mRNA → inhibits bacterial protein synthesis, leading to cell death.
- Environmental Factors: Antimicrobial activity is significantly enhanced in an alkaline environment and inhibited in acidic, purulent, or necrotic environments.
- Resistance: Because the transport mechanism requires oxygen, anaerobic bacteria are inherently resistant to all aminoglycosides.
Safety & warnings
Contraindications
- Known hypersensitivity to aminoglycosides
- Use with extreme caution in preexisting renal disease
- Use with caution in working dogs (e.g., seeing-eye, herding, hearing-impaired assistance dogs) due to irreversible ototoxicity
- Use with caution in patients with neuromuscular disorders (e.g., myasthenia gravis)
- Do not use in animals with botulism
- Use with caution in rabbits (adversely affects GI flora)
- Use with caution in neonates, geriatrics, and dehydrated patients
- Perforated tympanum (for aural preparations)
- Concurrent use of other nephrotoxic drugs
- Systemic use exceeding 7 days
- Pregnancy
Adverse effects
- Nephrotoxicity (tubular necrosis)
- Ototoxicity (auditory and vestibular; cats are highly sensitive to vestibular effects)
- Facial edema
- Pain or inflammation at the injection site
- Peripheral neuropathy
- Hypersensitivity reactions
- Rarely: GI signs, hematologic, and hepatic effects
- Nephrotoxicity (acute tubular necrosis)
- Neuromuscular blockade (rare)
- Delayed epithelial healing of corneal ulcers (ophthalmic use)
- Local irritation
Precautions
Aminoglycosides are eliminated primarily through renal mechanisms; use cautiously with serum monitoring and dosage adjustments in neonatal or geriatric animals. Sighthound dogs have significantly smaller volumes of distribution and may require reduced dosages. IM injections in horses can cause muscle irritation; IV is preferred. Monitor for antibiotic-associated diarrhea/colitis in horses (may promote Beta-2 toxin production by C. perfringens).
Drug interactions
Synergistic effects against some bacteria; however, potential for in vitro inactivation of aminoglycosides (do not mix in the same syringe/bag) and in vivo inactivation in patients with renal failure.
Potential additive nephrotoxicity (well documented with older cephalosporins like cephalothin).
Concurrent use may increase the nephrotoxic or ototoxic potential of aminoglycosides.
Increased risk for nephrotoxicity.
Concomitant use could potentiate neuromuscular blockade.
Increased risk of nephrotoxicity and ototoxicity
Increased risk of nephrotoxicity and ototoxicity
In vitro chemical inactivation (do not mix in same syringe)
Enhanced neuromuscular blockade
Monitoring
- Clinical efficacy (resolution of clinical signs, negative cultures)
- Renal toxicity: Baseline and ongoing urinalysis (casts in urine are often the initial sign of impending nephrotoxicity), serum BUN, and creatinine
- Gross monitoring for vestibular (balance) or auditory (hearing) toxicity
- Therapeutic Drug Monitoring (TDM): Serum levels drawn at 1, 2, and 4 hours post-dose. Peak should be >20 mcg/mL; 4-hour trough should be <10 mcg/mL
- Urinalysis (monitor for cellular casts as an early indicator of tubular damage)
- Serum creatinine and BUN
- Hydration status
- Therapeutic Drug Monitoring (TDM): Peak >20 μg/ml, Trough <1 μg/ml
- Auditory and vestibular function
Pharmacokinetics
Half-life
Absorption
Not appreciably absorbed after oral or intrauterine administration. Absorbed from topical administration during surgical irrigations. Bioavailability from extravascular injection (IM or SC) is >90%. Peak levels occur 0.5 to 1 hour after IM administration.
Distribution
Distributed primarily in extracellular fluid. Accumulates in inner ear and kidneys. Minimal protein binding (<20%). Does not readily cross the blood-brain barrier or penetrate ocular tissue. Vd is 0.15-0.3 L/kg in adult dogs/cats, and 0.26-0.58 L/kg in horses. Crosses the placenta.
Metabolism
Not significantly metabolized.
Elimination
Eliminated almost entirely by glomerular filtration. Patients with decreased renal function can have significantly prolonged half-lives.
Overdose
In the event of an inadvertent overdose, three treatments are recommended:
- Hemodialysis: Very effective in reducing serum levels, but rarely a viable option in veterinary medicine.
- Peritoneal dialysis: Reduces serum levels but is much less effective than hemodialysis.
- Complexation: Administration of ticarcillin (12-20 g/day in humans) is reportedly nearly as effective as hemodialysis in complexing and deactivating the drug.
Available products
Formulations
- Injection (100 mg/mL, 40 mg/mL, 10 mg/mL, 5 mg/mL, etc.)
- Oral solution (5 mg/mL)
- Soluble powder
- Ophthalmic preparations
- Otic preparations
- Topical preparations
- Injectable solution: 40 mg/ml, 100 mg/ml
- Ophthalmic gel: 0.3% w/w
- Ophthalmic drops: 0.5% w/v
- Aural drops/ointment: Combination products (e.g., with miconazole/hydrocortisone or clotrimazole/betamethasone)
Veterinary
- Gentamicin Sulfate Injection: 100 mg/mL (horses, poultry)
- Gentamicin Sulfate Injection: 5 mg/mL (piglets)
- Gentamicin Sulfate Oral Solution: 5 mg/mL (swine)
- Gentamicin Soluble Powder: 333.33 mg/g and 2 g/30 g (swine)
- Ophthalmic, otic, and topical preparations
- Clinagel Vet (Ophthalmic)
- Easotic (Aural combination)
- Genta (100 mg/ml Injectable)
- Otomax (Aural combination)
- Tiacil (Ophthalmic)
Human-labeled
- Gentamicin Sulfate Injection: 40 mg/mL, 10 mg/mL, 0.8 mg/mL, 0.9 mg/mL, 1 mg/mL, 1.2 mg/mL, 1.4 mg/mL, 1.6 mg/mL
- Topical, otic, and ophthalmic preparations
- Genticin (40 mg/ml Injectable)
Regulatory status
POM-V / POM status
POM-V / POM status
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store injection and oral solutions at room temperature (15-30°C); avoid freezing or temperatures above 40°C. Store soluble powder from 2-30°C. Do not store or offer medicated drinking water in rusty containers, as the drug may be destroyed.
Client information
Gentamicin is a powerful antibiotic reserved for serious infections.
- Administration: If you are instructed to give subcutaneous (under the skin) injections at home, ensure you have received proper training from your veterinary team.
- Toxicity Risks: This medication carries a significant risk of kidney damage (nephrotoxicity) and hearing/balance issues (ototoxicity).
- What to Watch For: Contact your veterinarian immediately if you notice your pet drinking more water than usual, urinating more or less frequently, vomiting, losing their appetite, showing signs of deafness, or exhibiting a head tilt, stumbling, or loss of balance.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.