Exploring the effects of high shear blending on lactose and drug using fluidised bed elutriation

Powder formulations comprising inhalation grade lactose and a mimic drug (cholesterol) were prepared using a high shear blending process for which the total energy input could be quantified. The formulations were fluidised in a classic fluidised bed system, to determine whether blending-induced changes could be determined through either bulk fluidisation behaviour or the characteristics of elutriated fractions from the powder beds. The evolution of the fluidisation regime within the powder beds (Δ pressure vs. superficial gas velocity) and total mass of elutriated material were not sensitive measures to differentiate between blended and unblended samples. However, blended and unblended material could be distinguished by the size distributions of the elutriated fractions. The study also showed that there were no further changes in the size distribution of the elutriated fractions once a chemically homogenous mixture of lactose and drug had been produced. However, further blending beyond this 'point of homogeneity' continued to change the lactose particle size distribution of the bulk powder; this may have implications for blend end point determination for these types of formulation.