Table 1.

Overview of the research pathway with the study components aimed at characterising the pharmacokinetics of nebulised tobramycin

Research pathway
Study	1. In vitro particle sizing and inhaled mass study	2. In vivo lung distribution study	3. In vitro microdialysis recovery study	4. In vivo lung microdialysis study
Aims	Describing and comparing the aerosol characteristics of two formulations of tobramycin	Comparing lung distribution of i.v. vs nebulised radiolabelled tobramycin 400 mg	Comparing relative recovery of vancomycin and tobramycin with microdialysis	Comparing ISF, ELF and blood concentrations of i.v. vs nebulised tobramycin 400 mg
Design	In vitro simulated adult mechanical ventilation using • Laser diffraction • Inhaled mass	Mechanically ventilated healthy ovine model	In vitro study using simulated in vivo conditions	Mechanically ventilated healthy ovine model
Materials and methods	• Size 9.0 mm I.D. ETT and tracheostomy tube • 4 ml tobramycin 100 mg/ml (400 mg) and 40 mg/ml (160 mg) • Vibrating mesh nebuliser just proximal to the Y- piece • Triplicate experiments	• Technetium-99m-labelled tobramycin 400 mg • i.v. administration (n = 1) • Nebulisation (n = 1) • CT scan to derive lung outline • Gamma camera scanning—dorsal, ventral, bilateral • Tissue and blood sampling	• Vancomycin 5 μg/ml • Tobramycin 5 μg/ml • In 50 ml FFP solution and constant stirrer • Perfusate flow rates 1, 1.5 and 2 μl/min • Sample collection every 20 min for 100 min (n = 5) • Triplicate experiments	• Bilateral thoracotomy approach for insertion of microdialysis catheters • i.v. tobramycin 400 mg (n = 1) • Nebulised tobramycin 400 mg (n = 1) • Bronchoalveolar lavage (1 and 6 h) • Intravascular microdialysis • Sample collection every 20 min for 8 h (n = 24)
Analysis	Particle size distribution parameters: • dv10 (μm) • dv50 (μm) • dv90 (μm) • FPF (%) Inhaled mass parameters: • Inhaled drug percentage (%) • Lung dose (mg)	• P/C ratio • Dorsal: ventral ratio • Right: left lung ratio • Upper: middle: lower lung zone • Quantitative analysis in the lung, liver, kidney, blood and urine specimens	• Relative recovery values for each of the flow rates	• ELF concentration and PK • ISF concentration and PK • Plasma concentration and PK

dv₁₀ volume diameter under which 10% of the sample resides; dv₅₀ volume median diameter; dv₉₀ volume diameter under which 90% of the sample resides; FPF fine particle fraction (particle size 1 to 5 μm); inhaled drug percent percent quantity of drug in the inhaled mass filter at the end of the tracheal tube post-nebulisation; lung dose the product of FPF and inhaled drug mass (mg); ELF epithelial lining fluid derived from urea levels; ISF interstitial space fluid; PK pharmacokinetics