Effect of texture on the intrinsic dissolution behaviour of acetylsalicylic acid and tolbutamide compacts

Preferred orientation of crystallites, i.e. texture, is a common result when a sample with an irregular habit of particles is compacted to form a tablet. Since texturization alters the random distribution of the crystal planes on the surface of the compacted sample, the dissolution properties of highly texturized tablets could differ from the properties of a tablet with a less preferred orientation. Three batches from both acetylsalicylic acid and tolbutamide were recrystallized using different crystallization parameters to obtain powders with different texturization behaviour. Several X-ray diffraction procedures were used to characterize the texture and other crystallographic properties of the samples. The intrinsic dissolution profiles were measured using the channel flow technique. In addition, the attachment energy of the crystal planes lying on the surface of the compacts was calculated theoretically. The results indicate that the most texturized compacts had a clearly lower intrinsic dissolution rate than the compacts with a lower degree of preferred orientation. By combining the results of the texture measurements with the calculated attachment energy values, the surface energies of the samples could be estimated and the estimated energy values were in agreement with the results of the dissolution studies. Moreover, it was found that by using the results of the texture measurements, the habit of the sample particles can be successfully predicted.