is an aminoglycoside antibiotic
used to treat various types of bacterial
infections, particularly Gram-negative
Mechanism of action
Tobramycin works by binding to a site on the bacterial 30S
and 50S ribosome
, preventing formation of the 70S complex. As a result, mRNA
cannot be translated
into protein and cell death ensues.
Tobramycin is preferred over gentamicin for Pseudomonas aeruginosa
pneumonia due to better lung penetration and bactericidal activity.
Like all aminoglycosides, tobramycin does not pass the gastro-intestinal tract
, so for systemic
use it can only be given intravenously
. This formulation for injection is branded Nebcin. Patients with cystic fibrosis
will often take an inhalational
form (Tobi) for suppression of Pseudomonas aeruginosa
infections. Tobramycin is also combined with dexamethasone
as an ophthalmic solution
Bausch & Lomb Pharmaceuticals, Inc. makes a sterile Tobramycin Ophthalmic Solution (eye-drops) with a tobramycin concentration of 0.3%, which is available by prescription only in the United States and Canada. (In some countries, such as Italy, it is available over the counter.) It is mixed with 0.01% benzalkonium chloride as a preservative. These concentrations result in 3 mg per ml and 0.1 mg per ml, respectively.
Like other aminoglycosides, tobramycin can cause deafness
or a loss of equilibrioception
(vertigo) in genetically susceptible individuals. These individuals have a normally harmless mutation in their DNA, that allows the tobramycin to affect their cells. The cells of the ear
are particularly sensitive to this.
Tobramycin can also be highly toxic to the kidneys, particularly if multiple doses accumulate over a course of treatment.
For these reasons, when tobramycin is given parenterally, it is usually dosed by body weight. Various formulae exist for calculating tobramycin dosage. Also serum levels of tobramycin are monitored during treatment.