UBC Theses and Dissertations

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UBC Theses and Dissertations

Effects of formulation variables and compression on drug release from beads coated using a pseudolatex dispersion of ethylcellulose Singh, Akaash


A modified, drug release system was developed in which a drug-layered, inert substrate (sugar spheres, NF) was coated with a membrane formed from a pseudolatex dispersion of ethylcellulose (Surelease®). This system has the same drug release profile regardless of encapsulation or compression into a disintegrating or a non-disintegrating tablet. The study examined the effects of substrate size, coating level and formulation with various external excipients on drug release from the compressed spheres. A preliminary investigation of the effects of some compression variables was also conducted. Compression of the coated spheres resulted in non-disintegrating tablets in which the ethylcellulose coating fused to form an apparent matrix. At the 10% Surelease® coating level, the rate of drug release from encapsulated spheres increased as sphere size decreased, however, release from the two intermediate sizes (20-25 and 30-35 mesh size) were similar. When compressed into non-disintegrating tablets, drug Release was fastest for tablets compressed from the largest spheres (14-18 mesh size). Release profiles from the three smaller sizes were similar (i.e. within 10%). When drug release was compared between encapsulated and compressed spheres of the same size, release was faster for tablets of the largest size, slower for tablets of the smallest size (45-60 mesh size) and similar for tablets of the two intermediate sizes. Little or no control of drug release was seen for disintegrating tablets made from 10% Surelease® coated spheres regardless of excipient used. When 30-35 mesh spheres were coated at Surelease® levels of 20 and 30%, drug release rate from encapsulated spheres was observed to decrease as coating level increased. Upon compression, drug release was fastest at the 10% coating level however, release profiles were similar at the 20 and 30% coating levels. Drug release profiles of encapsulated and compressed spheres were similar at each coating level. Compression of the 20% and 30% ethylcellulose coated, 30-35 mesh spheres with different excipients resulted in faster release of the model drug as compared to encapsulated spheres at the corresponding coating level indicating damage to the control release membrane. Apparent drug release for all of the formulations slowed as coating level increased regardless of diluent used. The most effective of the three diluent materials examined was Starch 1500® which produced tablets with the slowest release. Examination of compression factors such as tablet porosity, work of compression and peak offset time yielded inconclusive results. However, the tensile strength behaviour of the spheres with respect to compressional force at the three coating levels appeared to deviate from the trends observed for the uncoated and drug-layered spheres. This apparent deviation supports the concept of change in bonding mechanism but again appears inconclusive relative to the effects on drug release. As a direct match in dissolution release profiles could not be found for the disintegrating formulations with the encapsulated and compressed spheres at the same ethylcellulose coating level, a mixed system was proposed. Ten percent Surelease® coated, 30-35 mesh size spheres were suggested for the hard gelatin capsule and the nondisintegrating tablet while the disintegrating tablet would be made from 30% Surelease® coated, 30-35 mesh size spheres compressed with Starch 1500®.

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