Abstract
Three different crystallization methods, i.e., the solvent change (SC) method, neutralization (NT) method and quasi-emulsion solvent diffusion (QESD) method, were employed to prepare agglomerated tolbutamide crystals (referred to as SC-A, SC-B, NT and QESD). Each of the agglomerated crystals or unagglomerated tolbutamide crystals (abbreviated as bulk) alone (single formulation), magnesium stearate (MgSt; a lubricant)-added single formulation sample (formulation A), and Kollidon CL (a disintegrating agent)-added formulation A samples (formulation B) were compacted into tablets by the direct tableting method. With the objective of elucidating the compressibility of these samples, the following parameters were analyzed : (1) the course of change in the powder bed volume as a function of the applied compression pressure, (2) the pressure-transmission ratio from the upper punch to the lower punch, (3) the course of decompression (ejection force) and (4) the tensile strength of the tablets determined by the diametric compression method. The results of each sample were compared.For each of the single-formulations, formulation A and formulation B, Kawakita's equation was able to be applied to each stage of the compaction process over the tested compression pressure range of 50-1500kg/cm2. The limiting value of the compaction ratio of the samples was higher in the order of SC-B>NT>SC-A>QESD>bulk, and each agglomerate showed much higher compressibility than the bulk. Although the agglomerates and bulk showed the same pressure-transmission ratio from the upper punch to the lower punch, the bulk showed a smaller ejection force during decompression. The agglomerates, whose primary crystal diameter is small, showed much larger tensile strength of the compacted tablet than the bulk. The addition of MgSt improved the compaction process, but it weakened the tensile strength of the compacted tablets, especially in the case of the bulk. The addition of Kollidon CL decreased the ejection force due to a decrease in the adhesion force of the tablet to the surface of the die wall. Because Kollidon CL suppressed the effect of MgSt, the tensile strength of the compacted tablets was increased.The above results revealed that the compressibility of the agglomerates, especially SC-B and NT, is much superior to that of the bulk, and that these agglomerates have the properties necessary for direct tableting. Moreover, formulation B was suggested to be useful as a practical formulation for direct tableting.
