Study objectives: To evaluate the efficiency and reproducibility of pulmonary delivery of an investigational tobramycin PulmoSphere formulation (PStob) [Inhale Therapeutic Systems; San Carlos, CA] by a passive dry powder inhaler, and to compare serum concentrations and whole-lung deposition with a commercial nebulized tobramycin product (TOBI; Chiron Corporation; Seattle, WA).
Design: A five-period, open-label, nonrandomized crossover study.
Participants: Fourteen healthy volunteers were studied, and 12 completed the study.
Interventions: PStob powder was manufactured using lipid-based PulmoSphere technology, producing highly dispersible porous particles. PStob was radiolabeled with 99mTc, and in vitro experiments confirmed it as a valid drug marker. To identify whole-lung distribution via scintigraphy, subjects inhaled contents of a single capsule (72 L/min) containing 25 mg of 99mTc-labeled PStob (13.5 mg of tobramycin free base) in periods 1 to 3. In period 4, subjects received 99mTc nebulized tobramycin, approximately 2.5 mL of 300 mg/5 mL. Deposition and blood samples were obtained. In period 5, six 25-mg doses of unlabeled PStob (81 mg of tobramycin base) were inhaled and blood samples were collected.
Measurements and results: Mean whole-lung deposition of PStob was 34 ± 6% and nebulized tobramycin was 5 ± 2%. Peak tobramycin concentration in serum (Cmax) values were 0.6 μg/mL with PStob and 0.28 μg/mL after nebulized tobramycin. Serum area under the curve was 4.4 μg × h/mL vs 2.1 μg × h/mL for nebulized tobramycin. Median time to Cmax for PStob was comparable to nebulized tobramycin.
Conclusions: The aerosol doses of PStob (25 mg and 150 mg) were well dispersed and tolerated. Serum drug concentrations matched scintigraphy data and were roughly twice that of the comparator. Intrasubject dose variability for three equivalent periods did not exceed 18% relative SD. PStob Cmax (0.6 μg/mL) was well below the toxic threshold (2 μg/mL).