|Tropical Journal of Pharmaceutical Research|
|Official Journal of Pharmacotherpy Group|
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Parameters to be Considered in the Simulation
of Drug Release from Aspirin Crystals and their Microcapsules
Florence E Eichie† and Roland S Okor
of Pharmaceutics and Pharmaceutical Technology, Faculty of Pharmacy, University
of Benin, Benin City, Nigeria
Journal of Pharmaceutical Research 2002; 1(2): 99-110
microparticles may be microencapsulated with water-insoluble polymers to obtain
controlled release, which may be further determined by the particle
distribution. The purpose of this study was to determine the drug release
parameters needed for the theoretical prediction of the release profiles of
single aspirin crystals and their microcapsules.
Four single crystals
of aspirin of varied weight and orthorhombic in shape or their microcapsules
also of varied weights were randomly selected for the study. The microcapsules
were walled with an acrylatemethacrylate copolymer (wall thickness, 11 μm).
The following parameters were evaluated: the order of release, the
dissolution rate constant, k (crystals), the diffusion coefficient, D
(microcapsules), the maximum release m¥
and time to attain it t¥.
These parameters were in
turn used to simulate the release profiles of hypothetical single particles of a
wide range size distribution, 0.3 – 1.4 mm at 0.1mm intervals.
The empirical single
crystals exhibited an initial zero order (93%; dissolution constant = 4.4 min-1)
followed by a first order release (6%; dissolution constant = 0.38 min-1).
Maximum release from each of the crystals was 99% of the initial particle
weight; thus m¥
was a constant fraction of the initial particle weight. A zero order release
consistent with a Fickian diffusion model was displayed by the single
microcapsules (diffusion coefficient, 5.4x10-4 mm2min-1).
At same particle weight the release parameters m¥,
and the slopes of the rate
order plots compared favourably with the theoretical data.
The study indicates that the
empirical release data on a few single particles can be used to predict the
release profiles of single particles of a wide range of size distribution. This
finding may be exploited in the prediction of drug release from polydisperse
Aspirin crystals, drug release, simulation, microcapsules
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|Last updated: January 15, 2003|