presents the release rate (Mehdizadeh, Toliate, Rouini, Abashzadeh and Dorkoosh 309). The formula for this is an integral form of the Higuchi equation:
where Q is the cumulative amount of drug released per unit area of the matrix, A is the total drug concentration in the matrix, dissolved and undissolved, D is the diffusion coefficient of the drug in the matrix, C8 is the solubility or saturation concentration of the drug in the matrix, and t is the time.
There is another version of the Higuchi equation, which is its differential form, and allows the calculation of the rate of release, dQ/dt, at any time:
where k is the release constant. A plot of dQ/dt against the reciprocal of the square root of time gives a straight line. The experimental sy
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