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Although drying is widely applied during the manufacturing of solid dosage forms, its potential effect on the product's (key) properties is often underestimated. Hence, the present study addresses drying related modifications of wet-extruded pellets comprising calcium stearate (CaSt, matrix former) and ibuprofen (model drug). After spheronization, the pellets were tray dried at different temperatures. The dried pellets were evaluated regarding their microstructure, the ibuprofen distribution, solid state modifications and the resulting in-vitro dissolution profiles. The ibuprofen distribution profiles along the pellets' cross-sections varied for the different drying conditions. The profiles turned from inhomogeneous to uniform with increasing drying temperature. Temperatures above 20°C yielded solid state modifications, including ibuprofen transition into the amorphous state and the formation of eutectic compositions. As none of the batches exhibited a high specific surface area associated with an open, well-interconnected pore system, the dissolution profiles were a function of the ibuprofen distribution. Differences in the solid state did not contribute to the dissolution behavior, since the CaSt matrix did not swell or dissolve in the dissolution medium. These findings show that drying may considerably affect the final product properties even for moderate drying conditions., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Experiments have been carried out to study the behavior of L-threonine (needle-like) crystals during agitated drying. For an L-threonine/water system the morphology of the crystals was monitored using light microscopy and image analysis. Analysis of the transient behavior of the crystal size and shape distribution showed that attrition and agglomeration took place simultaneously during the process. The variation of the operating conditions (temperature, agitation and vacuum) revealed that attrition dominated the drying process when the drying rate was low and/or the shear rate was high. For high drying rates and low shear rates, agglomeration became dominant. This study suggests that crystal redissolution had no significant impact on crystal morphology. It was also found that due to their needle-like shape, large L-threonine crystals were very sensitive to attrition. When attrition controlled the drying process, most of the particle size reduction took place below a critical moisture content of 4%. When agglomeration controlled the drying process, most of the crystal size enlargement occurred below a moisture content of 6%.