Indirect microwave heating to pharmaceutical excipients: Lactose hydrate

Research and study of crystal structure of materials provide valuable information for physical-chemical characterization. The indirect microwave heating (IMH) which is applied in inorganic materials with poor dielectric properties was optimized to achieve the dehydration of two types of alpha LH2O (Granulac 200 and Pharmatose DCL 11) in a microwave field with Pyrex glass as an indirect heating medium. Lactose monohydrate was chosen as a model substance to the study because of its polymorphic properties. The IMH produces dehydration of alpha LH2O but needs to overcome a power threshold and can be accelerated by increasing the microwave field. The IMH process is not a selective method to produce a specific lactose anomer. Structural changes in lactose were characterized by the Rietveld method which is mainly used in the characterization of mixtures of inorganic materials. With this method, it was possible to quantify differences in the contribution of anhydrous lactose anomers. This methodology (IMH and Rietveld method) might be used for different hydrates or solvates of a given compound, which opens the possibility, at least theoretically, of characterization of samples with different anomeric stoichiometries or new molecular packing. (C) 2012 Elsevier B.V. All rights reserved.