How do we model this problem?
We decided to use STELLA to build the inital model because both of us were familiar with it and we felt that the multicompartment model would be easier to handle graphically. STELLA uses a graphical interface to assemble equations that approximate the behavior of the drug over time. The drug moves from one form, or stock, to another through flows. The pharmacokinetics research that we did allowed us to define these flows to represent the way penicillin actually moves through the body. Below is a graphic of the STELLA model.
Explaining the Model
Initially the penicillin is taken orally. The amount taken and dosage frequency can be varied. Some of this penicillin is available for absorption. The movement from the GI tract to the plasma is controlled by the absorption rate. Then from the bloodstream three different things could happen to the penicillin. Some of it is excreted unchanged. Another percentage is metabolized, meaning that the penicillin is changed into another type of molecule. Another fraction is bound to proteins. As long as the penicillin is in the plasma it does its job of preventing cell wall formation, thus preventing the spread of the bacteria. The excretion rate depended on the volume of distribution, the amount excreted from the kidneys and the concentration of the penicillin. The plasma concentration, which determines whether or not a theraputic level has been reached, is calculated from the amount of drug in the plasma and the volume of tissue through which the drug is distributed.
[Penicillin and You] [Application] [Algorithm] [Architecture] [Run the Model]
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