Pulmonary Spray Dried Powders of Tobramycin Containing Sodium Stearate to Improve Aerosolization Efficiency

Tobramycin microparticulate powders containing the hydrophobic adjunct sodium stearate were studied for their use as pulmonary formulations in dry powder inhalers. Spray-dried powders were characterized in terms of particle size distribution, morphology, crystallinity, drug dissolution rate, toxicity on epithelial lung cells and aerosol efficiency. The presence of the sodium stearate had a direct influence on the aerosol performance of tobramycin spray-dried powders. Powders containing 1% w/w sodium stearate had fine particle fraction FPF of 84.3±2.0% compared to 27.1±1.9% for powders containing no adjunct. This was attributed to the accumulation of sodium stearate at the particle surface. Powders with higher sodium stearate concentrations (2% w/w) showed significantly lower FPF (66.4±0.9%) and less accumulation of sodium stearate at the particle surface. This was attributed to the formation of adjunct micelles, which remained internalised in the particle structure due to their reduced tropism toward the drying drop surface and molecular mobility. Preliminary analysis of the toxicity effect of sodium stearate on A549 cell lines showed that the adjunct, in the concentration used, had no effect on cell viability over a 24-h period compared to particles of pure tobramycin. Tobramycin pulmonary powders with low level of sodium stearate, presenting high respiration performances and no over toxicity on lung cells, could be used to improve therapeutic outcomes of patient with Cystic Fibrosis.