In steady state drug treatment two aspects are important. First, the mean plasma concentration is determined by the dose per day. The relation between dose and plasma concentration is linear: at double dose the mean plasma concentration also doubles.

Second, fluctuations in the curve are determined by the frequency of administration. With the same total dose per day, a higher frequency of administration gives fewer fluctuations in the curve (Figure 17). With a continuous infusion there are no fluctuations at all.

Figure 17: Dose dependent fluctuations in the Cp/time curve

If you decide to raise the dose it will again take about 4 half-lives before you reach the new steady state. The same applies when you decrease it by giving a lower dose.