The Importance of Boundary Conditions in the Simulation of Dissolution in the USP Apparatus

N. McMahon, M. Crane, H. J. Ruskin and L. J. Crane.

Simul Model Pract Th. 15 (3) (2007) 247-255.


Abstract: The dissolving compact, or tablet, is the most widely used method of drug delivery. Dissolution tests are used to ensure consistency during tablet manufacture, to assess the dissolution characteristics of a particular tablet design, to establish in vitro/in vivo correlations, and to predict how the drug will perform in the body.

Dissolution tests also form a part of the drug approval process. The United States Pharmacopeia (USP) Type 2 Paddle Dissolution Apparatus, from here on referred to as the USP apparatus, is a standard dissolution test device, used by the Food and Drug Administration (FDA)and the pharmaceutical industry. Although the USP apparatus is much used, detailed theoretical descriptions of its characteristics are still not well developed.

This work considers one possible end state of a dissolving tablet, i.e. fragmentation into small particles with dissolution continuing from the disintegrated solid masses. A framework for calculating the motion of and mass transfer from a drug particle moving through the USP apparatus is outlined.

Calculations demonstrate that small particles move with the USP apparatus flow and that, for small particles below a critical diameter of about 200 microns, natural convection and radial diffusion dominate, i.e. forced convection effects can be neglected for small particles.

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