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Amorphous forms of poorly soluble drugs are more frequently being incorporated into solid dispersions for administration and extensive research has led to a reasonable understanding of how these dispersions, although still kinetically unstable, improve stability relative to the pure amorphous form. There remains however a paucity of literature describing the effects on such solid dispersions of subsequent processing into solid dosage forms such as tablets. This paper addresses this area by looking at the effects of the addition of common excipients and different manufacturing routes on the stability of a spray-dried dispersion (SDD) of the cannabinoid CB-1 antagonist, ibipinabant. A marked difference in physical stability of tablets was seen with the different fillers with microcrystalline cellulose (MCC) giving the best stability profile. It was found that minimising the number of compression steps led to improved formulation stability with a direct compression process giving the best results. Increased levels of crystallinity were seen in coated tablets most likely due to the exposure of the amorphous matrix to moisture and heat during the coating process. DSIMS analysis of the SDD particles indicated increased levels of polymer on the surface.

This study investigates the impact of micronization on the measured surface energy characteristics of an active pharmaceutical ingredient (API), ibipinabant, by inverse gas chromatography (IGC) using both a fixed probe concentration, commonly used in standard IGC methods, and a fixed probe surface coverage approach applied by the surface energy analyzer (SEA), a next generation IGC system. The IGC measurements indicate an initial increase in surface energy, going from un-micronized to micronized, followed by a reduction in surface energy with increasing micronization extent. This was attributable to the change in the retention behaviour of the dispersive probes as a consequence of the change in the probe surface coverage rather than a change in the actual surface energy of the materials being analysed. It was observed in the SEA data that micronization leads to an increase in the measured dispersive surface energy of the drug substance with increasing micronization extent. The increase in surface energy is primarily due to the generation of new, higher energy interaction sites, although a small additional increase is also observed which is related to the increase in the number and distribution of high energy sites. The results demonstrate that in order to obtain comparable surface energetic data between batches with varied surface area, and presumably between different materials, results should be obtained at a specific, and constant, probe surface coverage., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The solid-state physical stability and recrystallization kinetics during storage stability are described for an amorphous solid dispersed drug substance, ibipinabant, at a low concentration (1.0%, w/w) in a solid oral dosage form (tablet). The recrystallization behavior of the amorphous ibipinabant-polyvinylpyrrolidone solid dispersion in the tablet product was characterized by Fourier transform (FT) Raman spectroscopy. A partial least-square analysis used for multivariate calibration based on Raman spectra was developed and validated to detect less than 5% (w/w) of the crystalline form (equivalent to less than 0.05% of the total mass of the tablet). The method provided reliable and highly accurate predictive crystallinity assessments after exposure to a variety of stability storage conditions. It was determined that exposure to moisture had a significant impact on the crystallinity of amorphous ibipinabant. The information provided by the method has potential utility for predictive physical stability assessments. Dissolution testing demonstrated that the predicted crystallinity had a direct correlation with this physical property of the drug product. Recrystallization kinetics was measured using FT Raman spectroscopy for the solid dispersion from the tablet product stored at controlled temperature and relative humidity. The measurements were evaluated by application of the Johnson-Mehl-Avrami (JMA) kinetic model to determine recrystallization rate constants and Avrami exponent (n = 2). The analysis showed that the JMA equation could describe the process very well, and indicated that the recrystallization kinetics observed was a two-step process with an induction period (nucleation) followed by rod-like crystal growth., (Copyright © 2011 Wiley-Liss, Inc.)