Pharmaceutical Technology: Controlled Drug Release, Volume 2

134 CH. 12] BIODEGRADABLE POLYMERS
Fig. 2—Influence of the duration of thermal treatment on the drug release from tablets containing 15% HMW, DL-
PLA, 25% theophylline and 60% microcrystalline cellulose.
microcrystalline cellulose as the filler. At this concentration, microcrystalline cellulose can act as
a wicking agent which may promote disintegration of the tablet matrix [10]. However, the binding
capacity of the high molecular weight DL-PLA in the thermally treated tablets appeared to
counteract the disintegration effect of microcrystalline cellulose and to hold the tablet matrix
intact. Compaction studies demonstrated that the thermally treated tablets were significantly harder
than the non-thermally treated tablets, which suggested better binding. Thus, it is possible that
thermal treatment increases the binding capacity within the tablet resulting in a slower release rate
of drug from the tablet matrix, especially above the glass transition temperature of the polymer.
Dissolution profiles from tablets containing 60% theophylline and 25% microcrystalline
cellulose showed a smaller difference in the release rate of theophylline from heated and nonheated
tablets (Fig. 3). Nevertheless, both of these tablets demonstrated a matrix-controlled
release. These results suggest that the level of excipient in the tablet exerted a significant effect on
the dissolution release properties of thermally and non-thermally treated tablets. As the
microcrystalline cellulose content increased, the difference in release rates between heated and
non-heated tablets became more pronounced.
Dissolution studies were also conducted on tablets containing high molecular weight PCL-300
and PCL-700 (Fig. 4). As with the high molecular weight DL-PLA formulations, there was a
significant retardation in release rate of theophylline from thermally treated tablets when
compared with the non-thermally treated tablets.