What Is Gentamicin? Uses, Dosage, and What You Need to Know in 2026

Gentamicin is one of medicine's most established antibiotics, in clinical use since the 1960s. Despite its age, it remains a critical tool in treating some of the most serious bacterial infections — including those caused by bacteria resistant to many other antibiotics. This guide covers everything you need to know about gentamicin in 2026: what it is, what it treats, how it's given, and what to be aware of if you're prescribed it.

What Is Gentamicin?

Gentamicin is an aminoglycoside antibiotic derived from Micromonospora purpurea, a soil-dwelling actinomycete bacterium first discovered in the 1960s. It belongs to the same antibiotic family as tobramycin, amikacin, neomycin, and streptomycin. Aminoglycosides are known for their rapid, powerful killing of bacteria — particularly gram-negative organisms — and their ability to act even when bacteria are growing rapidly.

Gentamicin is a generic medication. The brand name for the injectable form was Garamycin. For eye preparations, the brand Gentak is still marketed. For topical use, it may be sold under the name Gentafair or as generic cream/ointment. It is available only by prescription.

What Does Gentamicin Treat?

The FDA has approved gentamicin for treating serious bacterial infections caused by susceptible gram-negative and some gram-positive organisms. Approved uses include:

Bacterial septicemia (bloodstream infection) including in newborns

Bacterial meningitis (infection of the membranes around the brain and spinal cord)

Serious urinary tract infections caused by gentamicin-susceptible organisms (not first-line for simple UTIs)

Gastrointestinal tract infections including peritonitis (infection of the abdominal lining)

Soft tissue, skin, and bone infections caused by susceptible bacteria

Bacterial endocarditis (heart valve infection) — used in combination with beta-lactam antibiotics for synergistic effect

Eye infections (ophthalmic form): Bacterial conjunctivitis, blepharitis, corneal ulcers, and external ocular infections

Skin infections (topical form): Superficial skin infections, infected wounds, and burns

What Forms Does Gentamicin Come In?

Gentamicin is available in multiple forms depending on the type and location of the infection:

Injectable (IV/IM): 10 mg/mL and 40 mg/mL solutions in vials. Used in hospitals and home infusion. This is the form used for serious systemic infections.

Ophthalmic solution (eye drops): Gentamicin 0.3% drops (Gentak), 5 mL bottle. Typically 1–2 drops in affected eye(s) every 4 hours.

Ophthalmic ointment: Gentamicin 0.3% ointment (Gentak), 3.5g tube. Applied as a half-inch ribbon 2–3 times per day.

Topical cream/ointment: Gentamicin 0.1% cream or ointment. Applied to the affected skin area 3–4 times daily. Available in 15g tubes.

How Is Gentamicin Dosed?

Dosing of injectable gentamicin is complex and requires careful calculation and monitoring. Key principles:

Traditional dosing: 3–5 mg/kg/day divided every 8 hours for adults. Children receive 6–7.5 mg/kg/day. Neonates: 7.5 mg/kg/day.

Extended-interval (once-daily) dosing: 5–7 mg/kg once every 24–48 hours (based on renal function). This approach takes advantage of gentamicin's concentration-dependent killing and post-antibiotic effect, maximizing efficacy while reducing toxicity risk.

Therapeutic drug monitoring (TDM): Gentamicin levels must be measured in the blood to ensure the dose achieves the target concentration without causing toxicity. Monitoring is required for treatment expected to last more than 48 hours.

Renal dosing adjustment: Dose must be reduced or the interval extended in patients with kidney impairment. GFR is used to guide adjustments.

What Bacteria Does Gentamicin Kill?

Gentamicin is active against a wide range of gram-negative bacteria, including:

Pseudomonas aeruginosa (including many drug-resistant strains)

Escherichia coli (E. coli)

Klebsiella, Proteus, Enterobacter, Serratia, and Citrobacter species

Staphylococcus species (gram-positive) — often used in combination with beta-lactams

Gentamicin is NOT effective against Streptococcus pneumoniae, most Enterococcus species (used in combination with beta-lactams for synergy), most anaerobic bacteria, Salmonella, or Shigella.

Key Safety Information

Gentamicin injectable carries a Black Box Warning for nephrotoxicity (kidney damage) and ototoxicity (hearing and balance damage). These risks apply to the injectable form and are monitored with regular blood tests and drug level checks during treatment. See our full guide on

Gentamicin side effects for what to watch for. Gentamicin is also contraindicated in pregnancy (FDA Category D).