The effect of egg albumin on the crystalline properties of carbamazepine in sustained release hydrophilic matrix tablets and in aqueous solutions

The influence of egg albumin (EA) on the crystal habit properties of carbam azepine (CBZ) in aqueous solutions, solid-state, and in sustained release m atrix tablets was investigated using differential scanning calorimetry (DSC ), hot-stage microscopy (HSM), X-ray powder diffraction (XRD), scanning ele ctron microscopy (SEM) and contact angle goniometer (CAG), The results sugg est that in solid-state mixtures, EA affected the polymorphic transitions o f CBZ from the beta to the alpha form. in hydrated matrix tablets and aqueo us solutions, EA influenced the conversion rate of CBZ to the dihydrate for m depending on EA concentration. It was found that increasing EA concentrat ion enhanced CBZ dihydrate aggregation, an effect that leads to the formati on of crystals with high mechanical strength and decrease of CBZ solubility . Possible mechanisms, which explain crystal growth and aggregation, as wel l as alteration of CBZ polymorphic transitions in the solid-state, gel laye r, and in aqueous solution were suggested. In the gel layer of hydrated tab lets the kinetics of CBZ transformation to the dihydrate form, crystal grow th and aggregation were influenced by various processes: matrix hydration, erosion mechanism and the formation of metastable conditions, which favor a ggregation and growth. The release kinetics of CBZ from the matrix highly c orrelated with the crystalline and morphological changes occurring in the m atrix. (C) 2000 Published by Elsevier Science B.V. All rights reserved.