Controlled Release of a Drug

by William Saxon

Submitted : Spring 2012

Many times it is desirable to have a drug released to the body over a period of time rather than all at once. For medication taken orally, this can be done by surrounding the drug with a membrane that is permeable both to the drug and to water. Many times it is desirable to have a drug released to the body over a period of time rather than all at once. For medication taken orally, this can be done by surrounding the drug with a membrane that is permeable both to the drug and to water. The goal of this project is to specify the size of the particle so that a drug is delivered to the body at a specified rate.  The diffusion coefficient of the drug theophylline through a membrane of ethylcellulose is D = 1.2 x 10^-10 cm²/s.  Assuming a membrane thickness of 0.0005 cm, determine the particle radius R_o that would result in 50% depletion of the drug in the particle in a time period of 2700 sec (3/4 of an hour).  Using [this radius] plot C_i/C_i^o as a function of time. Suppose the time period between medication doses is to correspond to the time at which the previous dose has been 95% deplete. What should the time period be between doses?

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