Spectrum of susceptibility
Tobramycin has a narrow spectrum of activity and is active against Gram-positive Staphylococcus aureus and various Gram-negative bacteria. Clinically, tobramycin is frequently used to eliminate Pseudomonas aeruginosa in cystic fibrosis patients. The following represents the minimum inhibitory concentration (MIC) susceptibility data for a few strains of Pseudomonas aeruginosa:

Pseudomonas aeruginosa -  <0.25 µg/mL – 92 µg/mL [ref?] Pseudomonas aeruginosa (non-mucoid) – 0.5 µg/mL - >512 µg/mL [ref?] Pseudomonas aeruginosa (ATCC 27853) – 0.5 µg/mL – 2 µg/mLThe MIC for Klebsiella pneumoniae, KP-1, is 2.3±0.2 µg/mL at 25 °C [unpublished]. Contraindications
Tobramycin is contraindicated in people with hypersensitivity against aminoglycoside antibiotics. The Infusion is also contraindicated in people with myasthenia gravis. Side effects
Like other aminoglycosides, a major side effect for tobramycin is ototoxicity or a loss of equilibrioception, or both in genetically susceptible individuals. Other side effects include nephrotoxicity, neuromuscular toxicity, and hypersensitivity reactions. Nephrotoxicity 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. Interactions
Muscle relaxants and diethylether can add to the neuromuscular blocking effects of tobramycin.Methoxyflurane, when used as an inhalational anesthetic, can aggravate the nephrotoxic effects of injected tobramycin.
Tobramycin passes the placenta: in the fetus, 20% of the mothers concentrations have been measured.The substance is neither bound to plasma proteins, nor is it metabolized. It is excreted in unchanged form via the kidneys with a biological half-life of about 2 to 3 hours. Elimination from deep compartments such as the renal cortex follows after 8 to 12 hours. In newborns the half-life is 4.6 hours on average; in those with a low birth weight it is as long as 8.7 hours on average. People with reduced kidney function also have a longer half-life for tobramycin, while in those with severe burns it can be shorter. References
Further reading
Davis BD (September 1987). "Mechanism of bactericidal action of aminoglycosides". Microbiological Reviews. 51 (3): 341–50. doi:10.1128/MMBR.51.3.341-350.1987. PMC 373115. PMID 3312985. External links
"Tobramycin". Drug Information Portal. U.S. National Library of Medicine.