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Software & Consulting For The Pharmaceutical Scientist |
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The figure below is intended to illustrate how INTELLIPHARM®PKCR Software simulates dissolution and absorption. Dissolution and absorption occur from a plug of intestinal fluid moving down the gastrointestinal tract. Time defines the position of the plug. As the plug moves down the gastrointestinal tract, the volume of the plug can change continuously due to water absorption or secretion. The mass transfer coefficient, generally referred to as the absorption rate constant even though it may not be constant, can also be changed continuously to reflect a position/time dependent change in the permeability of the gastrointestinal tract to the drug. The solubility can also be changed in a time dependent manner to reflect a position dependent change in pH that affects the solubility. If solubility falls below the concentration of dissolved drug, precipitation will be simulated. Features worth noting are the ability to simulate the dissolution of a polydisperse powder under non-sink conditions. This is illustrated by the different sized drug particles in the figure below. With time, the particles are getting smaller due to dissolution, and the concentration of drug in solution is increasing as illustrated in the darker shade of the plug with increasing time. If the concentration of drug in solution reaches the solubility, dissolution will stop until some drug has been absorbed. Eventually, the concentration of drug in solution will fall as absorption occurs and dissolution slows as the amount of solid drug is depleted. The controlled-release feature simulates the process of continuously releasing new drug particles with time as illustrated by the different colored particles. The amount released at each time point can also be changed continuously if desired. It should be noted that particles released at earlier times will affect the dissolution of particles released later by changing the concentration of drug in solution.
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© 2002-2007 Intellipharm, LLC |
