Particle synergy and aerosol performance in non-aqueous liquid of two combinations metered dose inhalation formulations: An AFM and Raman investigation

► Particle interactions in pMDI combination products (Symbicort and Seretide) were studied by AFM and Raman microscopy. ► Drug components in Symbicort (budesonide and formoterol) deposit on ACI plates as individual particles. ► Salmeterol and fluticasone tend to form aggregates. ► This tendency is evidenced with AFM measurements, and suggest a chemical synergy between salmeterol and fluticasone not present between formoterol and budesonide.