mass transfer Drug delivery from a matrix: Below is a matrix system for drug rel
ID: 968255 • Letter: M
Question
mass transfer
Drug delivery from a matrix: Below is a matrix system for drug release, as illustrated by Professor Lisa Brannon-Peppas. of the University of Texas at Austin. In such a system, the drug and polymer are mixed together to form a homogeneous matrix, and the drug passes from the polymer matrix into the external environment: Higuchi modeled the drug release from such a matrix using the following equation: Q = 2C_0(Dt/pi)^1/2 Where Q is the amount of drug released per unit area, Co is the initial concentration of drug in the matrix, D is the diffusively, and t is time. The Higuchi equation is also known as the "square squareroot" law of drug release. It is the most famous, and most often used, equation to describe drug delivery from a matrix. The Higuchi model makes some key assumptions about the matrix and the drug in order to create a simple model. Identify at least two of these assumptions. Explain how experimental data can be used to determine drug diffusively in a matrix, using the Higuchi model. What does the Higuchi model tell you about the rate of drug release over time? In other words, what is dO/dt? Does this make intuitive sense? If your goal is to achieve a constant rate of drug release over time, should you use a matrix for drug delivery? Why or why not?Explanation / Answer
Q = 2Co (D t / )1/2 .... (1)
a) The key assumptions are:
(i) The composition of the vehicle remains fixed during the diffusion process i.e., components other than the drug do not leave or enter the vehicle phase.
(ii) Diffusion constant of the drug is independent of time and position in the vehicle.
(iii) Drug reaching the receptor phase (skin) is absorbed instantaneously.
b)
By measuring experimentally the drug absorbed by the skin at different time intervals, the diffusivity constant D can be determined by fitting into equation (1).
c) Rate of drug release with time, dQ/dt = Co (D / t)1/2
This indicates that the rate of release of drug decreases with time and makes sense.
d) Release can be controlled by altering the diffusion coefficient, total drug concentration and drug solubility in the vehicle. Controlling these parameters is difficult to achieve a constant rate of drug release, use of matrix for drug release in not recommended.
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