Tobramycin !

An aminoglycoside close to gentamicin but more active against Pseudomonas aeruginosa; injected, or inhaled in cystic fibrosis.

Updated 2026-11-01

Class: Aminoglycosides
Target: Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
ATC code: J01GB01

Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunitTobramycin

The figure shows tobramycin bound to a short RNA that reproduces the A site of bacterial 16S rRNA, not a whole ribosome.

Target in 3D: Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit. PDB structure 1LC4 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Tobramycin binds the decoding site of the 30S ribosomal subunit and causes mRNA misreading and early termination of protein synthesis, which kills the bacterium. Its antibacterial activity and toxicity are very similar to gentamicin's, but it is the most active aminoglycoside against Pseudomonas aeruginosa.

Enters gram-negative bacteria through porins
Binds the A site of the 30S subunit
Misread proteins damage the bacterium
Concentration-dependent killing

Pharmacokinetics

Absorption: Injected (IV or IM) or inhaled; inhalation puts high levels in the airway with little absorption.
Distribution: Extracellular fluid; practically no protein binding.
Elimination: Unchanged in the urine by glomerular filtration; most of a dose is recovered within a day.
Half-life: About 2 hours with normal kidney function; it lengthens as creatinine clearance falls.

Indications

Serious infections by Pseudomonas aeruginosa and other gram-negative bacilli (septicemia, lower respiratory, urinary, intra-abdominal). Sepsis and septic shock →
Hospital-acquired pneumonia by gram-negatives, combined with a β-lactam. Hospital-acquired and ventilator-associated pneumonia →
Cystic fibrosis: injected in exacerbations and inhaled between them against chronic Pseudomonas. Cystic fibrosis →

Adverse effects

Common

Rising creatinine, casts in the urine
Tinnitus, dizziness

Contraindications

Hypersensitivity to tobramycin or another aminoglycoside

Key interactions

Loop diuretics (furosemide, ethacrynic acid): More ototoxicity; not given together.
Other nephrotoxic or neurotoxic drugs: Added kidney and nerve damage.
Neuromuscular blockers, anaesthetics: Risk of prolonged paralysis.

What is monitored

Peak and trough levels by protocol; a rising trough suggests accumulation
Creatinine and urinalysis
Hearing and balance; audiometry in older adults and long courses

Administration and safety

IV infusion or IM injection; not mixed with β-lactams in the same container.
Inhaled and injectable tobramycin are different products: the inhaled form is only nebulized and never injected.
Level samples at the exact times the protocol sets.

Nursing care

Baseline creatinine and hearing history; extra care in older adults.
Good hydration and urine output record.
Ask about tinnitus, hearing change and unsteadiness at every shift.

Pregnancy and breastfeeding

Aminoglycosides can cause fetal harm, including congenital deafness; systemic tobramycin is used in pregnancy only if the benefit justifies it.

Test yourself

Think of the answer, then tap the question to see it.

Which aminoglycoside is preferred when Pseudomonas aeruginosa is known or suspected?

Tobramycin, which has the best activity of the class against Pseudomonas.

Why is tobramycin inhaled in cystic fibrosis?

Inhalation delivers high levels to the airway, where Pseudomonas lives chronically, with little systemic exposure and less kidney and ear toxicity.

What does a rising tobramycin trough level suggest?

The drug is accumulating, often because kidney function is falling; the regimen is reviewed to avoid toxicity.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - TOBRAMYCIN injection (DailyMed (U.S. National Library of Medicine), 2026); Tobramycin Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 59 (McGraw Hill, 2023); RCSB PDB - 1LC4: Crystal Structure of Tobramycin Bound to the Eubacterial 16S rRNA A Site (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.