Tobramycin is an aminoglycoside antibiotic derived from Streptomyces tenebrarius and used to treat various types of bacteria infections, particularly Gram-negative infections. It is especially effective against species of Pseudomonas.
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 aeruginosapneumonia due to better lung penetration.
Like all aminoglycosides, tobramycin does not pass the gastro-intestinal tract, so forsystemic use it can only be given intravenously or intramuscularly. Ophthalmic (tobramycin only, Tobrex, or combined with dexamethasone, sold as TobraDex) and nebulised formulations both have low systemic absorption. The formulation for injection is branded Nebcin. The nebulised formulation (brand name Tobi) is indicated in the treatment of exacerbations of chronic infection with Pseudomonas aeruginosa in patients diagnosed with cystic fibrosis. A proprietary formulation of micronized, nebulized tobramycin has been tested as a treatment for bacterial sinusitis. Tobrex is a 0.3% tobramycin sterile ophthalmic solution is produced by Bausch & Lomb Pharmaceuticals. Benzalkonium chloride 0.01% is added as a preservative. It is available by prescription only in the United States and Canada. In certain countries, such as Italy, it is available over the counter. Tobrex and TobraDex are indicated in the treatment of superficial infections of the eye, such as bacterial conjunctivitis. Tobramycin (injection) is also indicated for various severe or life-threatening gram-negative infections : meningitis in neonates, brucellosis, pelvic inflammatory disease, Yersinia pestis infection (plague).
Like other aminoglycosides, tobramycin is ototoxic: it can cause hearing loss, or a loss ofequilibrioception, or both in genetically susceptible individuals. These individuals carry a normally harmless genetic mutation that allows aminoglycosides such as tobramycin to affect cochlear cells. Aminoglycoside-induced ototoxicity is generally irreversible.
As with all aminoglycosides, tobramycin is also nephrotoxic, meaning it is toxic to thekidneys. This effect can be particularly worrisome when multiple doses accumulate over the course of a treatment or when the kidney concentrates urine by increasing tubular reabsorption during sleep. Adequate hydration may help prevent excess nephrotoxicity and subsequent loss of renal function. For these reasons parenteral tobramycin needs to be carefully dosed by body weight, and its serum concentration monitored. Tobramycin is thus said to be a drug with a narrow therapeutic index.
Mass-spectrum of tobramycin
- “Tobramycin” (pdf). Toku-E. 2010-01-12. Retrieved 2012-06-11.
- “Nebulized Tobramycin in treating bacterial Sinusitis” (Press release). July 22, 2008. Retrieved 2009-12-06.
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