RESUMEN
BACKGROUND: Preservative-free tobramycin is commonly used as aerosolized therapy for ventilator associated pneumonia. The comparative delivery profile of the formulations of two different concentrations (100â¯mg/ml and 40â¯mg/ml) is unknown. This study aims to evaluate the aerosol characteristics of these tobramycin formulations in a simulated adult mechanical ventilation model. METHODS: Simulated adult mechanical ventilation set up and optimal settings were used in the study. Inhaled mass study was performed using bacterial/viral filters at the tip of the tracheal tube and in the expiratory limb of circuit. Laser diffractometer was used for characterising particle size distribution. The physicochemical characteristics of the formulations were described and nebulization characteristics compared using two airways, an endotracheal tube (ET) and a tracheostomy tube (TT). For each type of tube, three internal tube diameters were studied, 7â¯mm, 8â¯mm and 9â¯mm. RESULTS: The lung dose was significantly higher for 100â¯mg/ml solution (mean 121.3â¯mg vs 41.3â¯mg). Viscosity was different (2.11cp vs 1.58cp) for 100â¯mg/ml vs 40â¯mg/ml respectively but surface tension was similar. For tobramycin 100â¯mg/ml vs 40â¯mg/ml, the volume median diameter (2.02 vs 1.9⯵m) was comparable. The fine particle fraction (98.5 vs 85.4%) was higher and geometric standard deviation (1.36 vs 1.62⯵m) was significantly lower for 100â¯mg/ml concentration. Nebulization duration was longer for 100â¯mg/ml solution (16.9 vs 10.1â¯min). The inhaled dose percent was similar (30%) but the exhaled dose was higher for 100â¯mg/ml solution (18.9 vs 10.4%). The differences in results were non-significant for type of tube or size except for a small but statistically significant reduction in inhaled mass with TT compared to ET (0.06%). CONCLUSION: Aerosolized tobramycin 100â¯mg/ml solution delivered higher lung dose compared to tobramycin 40â¯mg/ml solution. Tracheal tube type or size did not influence the aerosol characteristics and delivery parameters.