TIME-DEPENDENT DENSIFICATION BEHAVIOR OF CYCLODEXTRINS

Understanding of volume reduction mechanisms is a valuable aid in the development of robust cyclodextrin tablet formulations. The particle a nd powder properties of alpha-, beta-, gamma- and hydroxypropyl (HP) - beta-cyclodextrins and their behaviour under compression were examined . The cyclodextrins studied showed big differences in particle-size di stribution and particle shape. The highest densification on tapping wa s found for cyclodextrins having the smallest particle size. Cyclodext rins were compressed using single-sided saw-tooth displacement-time pr ofiles at rates of 3 and 300 mm s(-1) with a compaction simulator. The densification of the powders was examined by Heckel treatment, using the tablet-in-die and ejected-tablet methods. The cyclodextrins were d enser at the beginning of the tableting process (at low pressures) if high rather than low velocity was used. Ranking according to their ten dency toward total deformation and permanent plastic deformation was: HP-beta-cyclodextrin > beta-cyclodextrin > gamma-cyclodextrin > alpha- cyclodextrin. The ranking order in strain-rate sensitivity (SRS) of to tal deformation was HP-beta-cyclodextrin >> gamma-cyclodextrin greater than or equal to alpha-cyclodextrin greater than or equal to beta-cyc lodextrin. On the basis of the yield pressure values and the Heckel pl ot profiles, all the cyclodextrins were highly prone to plastic deform ation. Cyclodextrins showed time-dependent consolidation behaviour man ifested as increased yield pressure with decreased contact time. A rat io was defined between the SRS of fast elastic recovery and total elas tic recovery. The two materials with high ratios, HP-beta-cyclodextrin and beta-cyclodextrin, were especially prone to fast elastic recovery with increasing punch velocities; gamma-cyclodextrin and alpha-cyclod extrin had low values and were less prone. On the basis of this parame ter it might be possible to categorize pharmaceutical materials accord ing to capping tendency.