Tobramycin as a pharmacologic tracer to compare airway deposition from nebulizers

Study Objective. To assess the utility of inhaled tobramycin as a pharmacologic tracer for comparing lung deposition from a prototypic breath-actuated jet nebulizer connected to an electronic pressure sensor designed to coordinate nebulization with inspiration with that from a continuously operating standard jet nebulizer. Design. Prospective open-label study. Setting. University-affiliated research center. Subjects. Six healthy adult volunteers. Intervention. All subjects received inhaled tobramycin 80, 160, and 320 mg from each nebulizer during six visits, as well as oral tobramycin 32 mg at a seventh visit to confirm the absence of significant gastrointestinal absorption. During each visit, urine was collected before drug administration and in 12-hour segments throughout the first 48 hours after administration. Measurements and Main Results. Lung deposition of tracer after each of the seven treatments was quantified by measuring urinary tobramycin excretion over 48 hours with use of an enzyme-multiplied immunoassay technique. The ratio of tobramycin excreted after breath-actuated nebulization to that after standard nebulization, normalized for dose, was used to compare lung deposition by the two devices. Urinary excretion of tobramycin was linear and proportional to dose for both nebulizers. For every 1 mg of tobramycin that the standard nebulizer deposited into the lungs, the breath-actuated nebulizer deposited 1.22 mg (95% confidence interval 1.04-1.43). Conclusions. Tobramycin can be used as a pharmacologic tracer for comparison of relative airway deposition by nebulizers.