Study of thixotropic bases for the filling of hard capsules

The purpose of this study was to define liquid or semi-solid excipient base s for the filling of hard capsules at room temperature. The rise of amphiph ilic bases rather than strictly hydrophobic or hydrophilic bases allows the rise of this pharmaceutical form to be extended to a wide range of active substances. The excipient mixtures used must have the thixotropic propertie s necessary to meet two essential requirements: perfect fluidity during dis tribution in the capsule filling machine and recovery of a consistency in t he resting capsule in order to prevent leaks. A methodology based on the si mulation of the rheological history of these mixtures from the capsule-fill ing machine to the capsule has been developed to forecast behaviour during and after filling. Rheological studies were carried out in permanent flow a nd oscillating mode. These allow analysis of the excipient flow in the caps ule-filling machine and evaluation of thixotropy recovery kinetics in rite capsule. At the same time, the behaviour of these bases was tested on a pil ot semi-automatic capsule-filling machine. All of these characteristics all owed a precise definition of the specifications of a preparation compatible with the "semi-solid content capsule" dosage form.