Open AccessJournal Article
Release of medroxyprogesterone acetate from a silicone polymer.
T. J. Roseman,William I. Higuchi +1 more
TLDR
In this paper, the physicochemical factors involved in the in vitro release of medroxyprogesterone acetate (MPA) a water-insoluble steroid embedded in a silicone rubber matrix was based upon a model system which considered the matric boundary diffusion layer.Abstract:
A study of the physicochemical factors involved in the in vitro release of medroxyprogesterone acetate (MPA) a water-insoluble steroid embedded in a silicone rubber matrix was based upon a model system which considered the matric boundary diffusion layer; extensive mathematical equations for the model are presented for planar and cylindrical cases. Initial and long-time release rates were obtained. Zones of MPA depletion were measured microscopically as a function of time and the partition coefficient of MPA was determined. Following relatively constant initial release rates a nonlinear dependence of release rates upon MPA concentration (3% 12% 24%) was found. As MPA diffused from the matrix well-defined zones of depletion developed and were photographed. Comparison of the present model to the T. Higuchi model of drug release (based on a purely matrix-controlled system) indicated that when boundary layer was considered a better fit of experimental data to theory was found. Findings suggest that the partition coefficient diffusion coefficients medroxyprogesterone acetate concentration within the polymer and agitation conditions play important roles in the release process. The applicability of the model to an in vivo system (in which slower release of MPA has been observed) is evaluated.read more
Citations
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Numerical simulation of controlled nifedipine release from chitosan microgels
TL;DR: Control nifedipine release from nonswellable chitosan sphere-based microgels is investigated numerically with a mathematical model that takes into account both drug dissolution and drug diffusion through the continuous matrices of the sphericalmicrogels.
Journal ArticleDOI
The Higuchi square root equation applied to matriceswith high content of soluble drug substance
TL;DR: In this article, it was shown that dissolution of a soluble drug in high concentration from an insoluble matrix follows the Higuchi square root equation, except an initial lag phase and a terminal diffusion phase.
Journal ArticleDOI
Modelling of drug release from pellets coated with an insoluble polymeric membrane
TL;DR: A model to accurately describe drug release kinetics from coated pellets where the membrane does not entirely control the release is proposed and the possibility of ab initio optimization, from easy experiments not including coated pellets: drug release from uncoated matrices and permeation kinetics through free films.
Journal ArticleDOI
Prolonged Release of Theophylline from Aqueous Suspensions
Joel L. Zatz,D. W. Woodford +1 more
TL;DR: In this article, the dissolution of theophylline from aqueous suspensions was measured by the U.S.P. paddle method, and diffusion cell studies suggested that transport within the formed matrix was due to diffusion through immobilized liquid water.
Journal ArticleDOI
Diffusion model for drug release from suspensions II: release to a perfect sink.
F. Tom Lindstrom,James W. Ayres +1 more
TL;DR: The predicted mass of drug released versus time curves using this model are in agreement with some reported experimental data but differ from predictions using the classical model for semisolid suspensions, in relation to the drug dissolution rate and diffusion rate in the vehicle.
References
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Mechanism of sustained‐action medication. Theoretical analysis of rate of release of solid drugs dispersed in solid matrices
TL;DR: The analyses suggest that for the latter system the time required to release 50% of the drug would normally be expected to be approximately 10 per cent of that required to dissolve the last trace of the solid drug phase in the center of the pellet.
Book
Membrane Technology and Applications
TL;DR: Overview of membrane science and technology membrane transport theory membrane and modules concentration polarization reverse osmosis ultrafiltration microfiltration gas separation pervaporation ion exchange membrane processes - electrodialysis carrier facilitated transport medical applications of membranes other membranes processed.
Journal ArticleDOI
A simple equation for description of solute release I. Fickian and non-fickian release from non-swellable devices in the form of slabs, spheres, cylinders or discs
TL;DR: In this paper, a simple exponential relation Mt/M∞ = ktn is introduced to describe the general solute release behavior of controlled release polymeric devices, where Mt is the fractional release, t is the release time, k is a constant, and n is the diffusional exponent characteristic of the release mechanism.