Tobramycin clinical pharmacology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Clinical Pharmacology
TOBI® is specifically formulated for administration by inhalation. When inhaled, tobramycin is concentrated in the airways.
Pharmacokinetics
TOBI® contains tobramycin, a cationic polar molecule that does not readily cross epithelial membranes.(1) The bioavailability of TOBI® may vary because of individual differences in nebulizer performance and airway pathology.(2) Following administration of TOBI®, tobramycin remains concentrated primarily in the airways.
Sputum Concentrations: Ten minutes after inhalation of the first 300-mg dose of TOBI®, the average concentration of tobramycin was 1237 µg/g (ranging from 35 to 7417 µg/g) in sputum. Tobramycin does not accumulate in sputum; after 20 weeks of therapy with the TOBI® regimen, the average concentration of tobramycin at ten minutes after inhalation was 1154 µg/g (ranging from 39 to 8085 µg/g) in sputum. High variability of tobramycin concentration in sputum was observed. Two hours after inhalation, sputum concentrations declined to approximately 14% of tobramycin levels at ten minutes after inhalation.
Serum Concentrations: The average serum concentration of tobramycin one hour after inhalation of a single 300-mg dose of TOBI® by cystic fibrosis patients was 0.95 µg/mL. After 20 weeks of therapy on the TOBI® regimen, the average serum tobramycin concentration one hour after dosing was 1.05 µg/mL.
Elimination: The elimination half-life of tobramycin from serum is approximately 2 hours after intravenous (IV) administration. Assuming tobramycin absorbed following inhalation behaves similarly to tobramycin following IV administration, systemically absorbed tobramycin is eliminated principally by glomerular filtration. Unabsorbed tobramycin, following TOBI® administration, is probably eliminated primarily in expectorated sputum.[1]
References
Adapted from the FDA Package Insert.