Physically, r is the factor by which the concentration of the drug is decreased during the time L between doses.
Figure 2: Safe drug concentration range
If the answer is no, can you achieve a satisfactory long-run level just by adjusting the time between doses? Just by adjusting the dose? Justify your answer. (Assume there is a simple way to tell just how much substance must be administered in order to raise the concentration by any given amount. That is, you can answer this question by specifying how much the concentration of the drug in the blood needs to be raised on each dose.)
is satisfied the drug can be safely and effectively administered by giving the same dose at regularly spaced time intervals. That is, there is a dosage program that keeps the drug concentration above m and below M indefinitely.