Computational fluid dynamics: applications in pharmaceutical technology - Computer-Aided Applications in Pharmaceutical Technology - page 249

from compact with all surfaces exposed. A signifi cantly lower dissolution
rate from the central position compared to the dissolution rates from
positions 1 and 2 was observed, regardless of the compact surface exposed.
There was greater variability in dissolution results in case of control
compacts that were not fi xed during testing than in compacts that were
fi xed to one of three positions. It was concluded that small changes in case
of position within the area, where a dosage form is usually located during
testing, can result in noticeable differences in dissolution rate. It was also
found that CFD can be successfully applied to the interpretation of the
results. Namely, higher velocities were observed around the compacts in
off-center positions than in a central position. Furthermore, CFD
simulations of the compacts in positions 1 and 2 showed variations in
velocity gradients in the vicinity of the compact surface that infl uenced the
shape of the compact during dissolution. It was suggested that this could
be important in cases of coated or layered dosage forms, because all
surfaces would not be exposed to equal hydrodynamic conditions and
therefore would not dissolve at equal rates (Figure 7.11).

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￿ ￿

Photograph of compact after undergoing dissolution
for 1 h in: (a) position 1 and (c) position 2. Velocity
vectors surrounding the compact in: (b) position 1 and
(d) position 2. Left side of the compact in (a) and (b) is
facing the center of the base of the vessel; the front of
the compact in (c) and (d) is facing the center of the
base of the vessel (reprinted from D'Arcy et al., 2005;
with permission from John Wiley & Sons)

Figure 7.11