چکیده (انگلیسی):

The purpose of this research was to evaluate triple layer,
donut-shaped tablets (TLDSTs) for extended release dosage
forms. TLDSTs were prepared by layering 3 powders sequentially
after pressing them with a punch. The core tablet
consisted of enteric polymers, mainly hydroxypropyl
methylcellulose acetate succinate, and the bottom and top
layers were made of a water-insoluble polymer, ethyl cellulose.
Drug release kinetics were dependent on the pH of
the dissolution medium and the drug properties, such as
solubility, salt forms of weak acid and weak base drugs,
and drug loading. At a 10% drug loading level, all drugs,
regardless of their type or solubility, yielded the same
release profiles within an acceptable level of experimental
error. As drug loading increased from 10% to 30%, the
drug release rate of neutral drugs increased for all except
sulfathiazole, which retained the same kinetics as at 10%
loading. HCl salts of weak base drugs had much slower
release rates than did those of neutral drugs (eg, theophylline)
as drug loading increased. The release of labetalol
HCl retarded as drug loading increased from 10% to 30%.
On the other hand, Na salts of weak acid drugs had much
higher release rates than did those of neutral drugs (eg,
theophylline). Drug release kinetics were governed by the
ionization/erosion process with slight drug diffusion,
observing no perfect straight line. A mathematical expression
for drug release kinetics (erosion-controlled system) of
TLDSTs is presented. In summary, a TLDST is a good
design to obtain zero-order or nearly zero-order release
kinetics for a wide range of drug solubilities.