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THE PHARMA REVIEW
(SEPTEMBER 2009) |
Mathematical Modeling of
Drug Release From Polymeric Devices- An Overview of
Widely Used Models - Theory, Implementation and
Rationale
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Ritu Mehra Gilhotra, Vishv
Priya Bhardwaj, Neeraj Gilhotra, D N Mishra |
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Abstract: Describing mode or mechanism of drug
release from developed polymeric system, meant to
delivery drug conventionally or in controlled manner, is
executed by applying various mathematical models
nowadays. The major advantages of these models are: (i)
the elucidation of the underlying mass transport
mechanisms; and (ii) the possibility to predict the
effect of the device design parameters (e.g., shape,
size and composition) on the resulting drug release
rate. Various Simple empirical or semi-empirical models
such as the classical Higuchi equation and the so-called
power law, as well as more complex mechanistic theories
that consider diffusion, swelling and dissolution
processes simultaneously are applied in dosage form
research to understand the mechanism and actual behavior
drug polymer matrix in dissolution testing. In the
present work, some frequently used models of drug
release from polymeric devices are discussed.
Introduction
Experimentation with new polymers and compositions of
many polymers to make carrier matrices of polymers to
sustain or prolong the drug release is highly practiced
in dosage form research. One way of achieving this is by
the incorporation of the drugs into polymers.
Drug-polymer systems can not only prolong the release of
a pharmacologic agent, but can also modulate the rate of
release of the drug to be dependent on the vehicle
itself rather than on the environmental conditions. High
reproducibility of the release profiles can also be
achieved by using a drug-polymer system. The advantages
of a controlled delivery device can be appreciated
further by comparing the idealized drug levels achieved
by conventional drug formulations (tablets and
injections) and those achieved from a polymeric
controlled drug delivery system. The goal of a
controlled release device is to maintain the
concentration of the drug between these two levels for a
prolonged period of time from a single dosage form. This
would alleviate the need for repeated doses and cause
fewer side effects. Controlled release drug delivery
systems enhance the safety, efficacy, and reliability of
drug administration. An ideal controlled drug delivery
system (DDS) is the one which delivers the drug at a
predetermined rate locally or systematically for a
specified period of time.
An Overview of Drug Release Mechanisms and Patterns
The overall drug release mechanism may be affected by
many factors such as polymer
Swelling, polymer erosion, drug dissolution / diffusion
characteristics, drug distribution
In matrix, drug polymer ratio & system geometry
(cylinder sphere so on) the following Phenomena are
involved -
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At the beginning of process ; firstly water comes in
the contact to the polymer & imbibed in to the
matrix .To describe this process this process
adequately ,it is imp. to consider :
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The exact geometry
of the device
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In case of cylinders
both axial and radial direction of the mass
transport &
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The significant
dependence of the water diffusion coefficient on
the matrix swelling ratio
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