tobramycin

tobramycin
IUPAC name	(2S,3R,4S,5S,6R)-4-Amino-2-{[(1S,2S,3R,4S,6R)-4,6-diamino-3-{[(2R,3R,5R,6R)-3-amino-6-(aminomethyl)-5-hydroxyoxan-2-yl]oxy}-2-hydroxycyclohexyl]oxy}-6-(hydroxymethyl)oxane-3,5-diol
Tradename	Tobi, others
Drugs.com	Monograph
MedlinePlus	a682660
Routes of administration	Intravenous, intramuscular, inhalation, ophthalmic
CAS number	32986-56-4
PubChem	36294
DrugBank	DB00684
ChemSpiderID	33376
UNII	VZ8RRZ51VK
ChEBI	100147
ChEMBL	1200455
ATC prefix	J01
ATC suffix	GB01, S01AA12, S02AA15
Legal status	Rx-only

tobramycin is an aminoglycoside antibiotic derived from the bacterium Streptomyces tenebrarius. It is primarily used to treat severe Gram-negative infections, particularly those caused by Pseudomonas aeruginosa, and is a cornerstone therapy for chronic pulmonary infections in patients with cystic fibrosis. The drug is marketed under brand names such as Tobi and is administered via intravenous injection, inhalation, or as an ophthalmic solution.

Medical uses

Tobramycin is indicated for the treatment of serious infections caused by susceptible strains of Pseudomonas aeruginosa, Escherichia coli, and Proteus species. It is a first-line agent for managing pulmonary exacerbations in individuals with cystic fibrosis, often delivered via a nebulizer such as the PARI eFlow. The ophthalmic formulation is used for external ocular infections involving the conjunctiva or cornea. It is also employed in combination with a beta-lactam antibiotic for synergistic effects in treating endocarditis caused by Enterococcus faecalis.

Adverse effects

The most significant adverse effects are nephrotoxicity and ototoxicity, which can lead to permanent hearing loss or vestibular dysfunction. These risks are heightened with prolonged use, high doses, or concurrent administration of other nephrotoxic drugs like vancomycin or furosemide. Other potential effects include neuromuscular blockade, which may be potentiated by anesthetic agents, and local reactions such as pain at the injection site. Monitoring of serum creatinine levels and auditory brainstem response is recommended during therapy.

Mechanism of action

As an aminoglycoside, tobramycin binds irreversibly to the bacterial 30S ribosomal subunit, specifically to the 16S rRNA component within the A site of the ribosome. This binding inhibits protein synthesis by causing misreading of the mRNA template and blocking the formation of initiation complexes. The action is concentration-dependent and results in bactericidal effects, particularly against aerobic Gram-negative bacteria. Its efficacy is reduced in anaerobic environments, such as abscesses, due to oxygen-dependent uptake.

Pharmacokinetics

Tobramycin is poorly absorbed from the gastrointestinal tract and is typically administered parenterally. It distributes widely into extracellular fluid, including synovial fluid and peritoneal fluid, but achieves poor penetration into the cerebrospinal fluid unless the meninges are inflamed. The drug is excreted almost entirely unchanged by glomerular filtration in the kidneys, with a half-life of approximately two hours in patients with normal renal function. Dosage adjustments are critical in patients with renal impairment or those undergoing hemodialysis.

History

Tobramycin was discovered in the 1960s from the actinobacterium Streptomyces tenebrarius by researchers at Eli Lilly and Company. It received approval from the U.S. Food and Drug Administration in the 1970s. Its development was part of a broader search for new aminoglycosides following the introduction of gentamicin. A significant advancement was the formulation of tobramycin for inhalation, which was pioneered in the 1990s through collaboration with the Cystic Fibrosis Foundation and dramatically improved management of chronic Pseudomonas infections.

Society and culture

Tobramycin is on the World Health Organization's List of Essential Medicines. The inhaled formulation, marketed as Tobi, has been the subject of extensive clinical trials conducted at institutions like the Johns Hopkins Hospital. The high cost of chronic therapy has been a point of discussion within healthcare systems such as the National Health Service. The drug's patent expiration has led to the availability of generic versions, increasing access in programs like the President's Emergency Plan for AIDS Relief.

Category:Aminoglycoside antibiotics Category:World Health Organization essential medicines