Atomic force microscopy (AFM) was used to investigate drug-carrier interactions between beclometasone dipropionate (BDP) and a series of untreated and modified lactose surfaces. This quantitative information was correlated with bulk characterization methods and an in-vitro study. Modified lactose surfaces were prepared using a proprietary process referred to as "particle smoothing" to obtain smooth carrier surfaces with or without the presence of magnesium stearate. The engineering of lactose carrier surfaces using the particle smoothing process resulted in significant differences in surface morphology when compared with the "as supplied" starting material. The energy of separation, between BDP and lactose samples, determined by AFM suggested similar lognormal distributions with a rank decrease in median separation energy (e(0.5)) (26.7, 20.6 and 7.7 microJ for untreated, particle-smoothed and particle-smoothed with magnesium stearate, respectively). A series of in-vitro twin stage impinger studies showed good correlation with the AFM separation energy measurements. The mean fine particle dose increased for the two processed lactose samples, with a significant increase for the lactose processed with magnesium stearate, 102.0+/-16 microg compared with 24.2+/-10.7 microg for the untreated lactose. Thus, the AFM presents as a possible pre-formulation tool for rapid characterization of particle interactions.
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