First, let A n denote the amount of drug in the system after dose n . Such an equation is well suited for use in a programmable calculator or a spreadsheet, especially in investigating the long-term behavior of the model. The recursion equation above can be translated into a spreadsheet to answer this. Students will notice that the peak levels, A n , don't get bigger indefinitely and can investigate ways of determining the limiting value. Suppose she doesn't like taking medicine, so she decides to take only one pill every 8 hours for 20 days.
Many drugs have what is known as a therapeutic level.
Unless the amount of drug in one's system reaches the therapeutic level, the drug is not effective. Sometimes doctors suggest that the patient take a double dose initially, called a loading dose. A simple variation in the standard model can illustrate the effect of the loading dose on the effectiveness of the drug. In addition to a therapeutic level, drugs also have a toxic level. If too much of the drug is in your system, you can become ill as a result.