Tobramycin microbiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Microbiology
Tobramycin is an aminoglycoside antibiotic produced by Streptomyces tenebrarius. It acts primarily by disrupting protein synthesis, leading to altered cell membrane permeability, progressive disruption of the cell envelope, and eventual cell death.
Tobramycin has in-vitro activity against a wide range of gram-negative organisms including Pseudomonas aeruginosa. It is bactericidal at concentrations equal to or slightly greater than inhibitory concentrations.
Susceptibility Testing
A single sputum sample from a cystic fibrosis patient may contain multiple morphotypes of Pseudomonas aeruginosa and each morphotype may have a different level of in-vitro susceptibility to tobramycin. Treatment for 6 months with TOBI® in two clinical studies did not affect the susceptibility of the majority of P. aeruginosa isolates tested; however, increased minimum inhibitory concentrations (MICs) were noted in some patients. The clinical significance of this information has not been clearly established in the treatment of P. aeruginosa in cystic fibrosis patients. For additional information regarding the effects of TOBI® on P. aeruginosa MIC values and bacterial sputum density, please refer to the CLINICAL STUDIES section.
The in-vitro antimicrobial susceptibility test methods used for parenteral tobramycin therapy can be used to monitor the susceptibility of P. aeruginosa isolated from cystic fibrosis patients. If decreased susceptibility is noted, the results should be reported to the clinician. Susceptibility breakpoints established for parenteral administration of tobramycin do not apply to aerosolized administration of TOBI®. The relationship between in-vitro susceptibility test results and clinical outcome with TOBI® therapy is not clear.[1]
References
Adapted from the FDA Package Insert.