Lamellar double hydroxides as pharmaceutical excipients: a compatibility study

Lamellar double hydroxides (LDH) are a class of inorganic materials widely used as pharmaceutical ingredients. However, their use as excipients and mainly as drug carriers lacks specific research in pharmaceutical technology, as there are no publications capable of defining the behavior of these materials as components of a formulation in the presence of other pharmaceutical adjuvants already consolidated. The purpose of the study was to evaluate the excipient–excipient compatibility of calcium and aluminum LDH (LDH–CaAl) against other excipients, including colloidal silicon dioxide (aerosil®), soluble starch (SS), microcrystalline cellulose 101 (MCC), magnesium stearate (MS), hydroxypropyl-beta-cyclodextrin (HPβCD), lactose monohydrate (LACM), sodium starch glycollate (SSG), PVP-K30 and talc. Initially, absorption spectroscopy in the infrared region with Fourier transform (FTIR) and thermogravimetry and differential thermal analysis (TG/DTA) was performed. When signs of possible interactions were observed, X-ray diffraction (XRD) was performed as a complementary technique. At the end of the study, the FTIR spectra and the TG curves of LDH–CaAl and each of the isolated excipients were compared with the analysis of the binary mixtures, where there is compatibility between LDH–CaAl and all excipients tested. Although the XRD has been used to assess evidence of interactions in mixtures with stearate, lactose, PVP and talc, the joint analysis of the results proved to be satisfactory. All these pioneering results suggest, therefore, the acceptability and suitability of LDH–CaAl as a potentially scalable excipient for the development of safe and rational dosage forms.