When the drug is absorbed rapidly after oral administration, all the administered dose can get into the systemic circulation before significant amount of the drug is eliminated.

In this case we can assume that the change in the drug concentration from Cp min ss to Cp max ss resulted from the administered dose. So, Cp max and Cp min can be (approximately) estimated similar to repeated iv doses.

Notice that fast absorption does not mean complete absorption, so, the drug bioavailability has to be considered.

The steady state is the condition when the rate of drug administration is equal to the rate of drug elimination.

When the drug is administered as a constant rate IV infusion, there will be one steady state concentration as long as the rate of administration and the rate of elimination do not change.

When drug administration involves repeated doses, the drug concentration-time profile during each of the dosing intervals ( τ ) will be identical at steady state. This means that the maximum, the minimum, and the average concentrations during each dosing interval will be similar at steady state.

Cpmax ss is the maximum drug concentration at steady state. This is the drug concentration right after oral drug administration (amount/volume).

Bioavailability is a measure of the fraction of the administration dose that reaches the systemic circulation.

Absolute bioavailability is the fraction of the total dose that reaches the systemic circulation. It can take values between zero when the drug is not absorbed at all to 1 when all the administered dose reaches the systemic circulation. The absolute bioavailability can be expressed in terms of percentage (0-100%).

The relative bioavailability is the bioavailability of a drug product relative to the bioavailability of another drug product (reference standard preparation). The relative bioavailability can take any value above zero. It can be more than one when the product under investigation has bioavailability higher than that of the reference standard.

Cpmax ss is the maximum drug concentration within one dosing interval at steady state. It is the drug concentration right after drug administration only when the drug is given as IV bolus or when the drug is rapidly absorbed after oral administration.

Cpmin ss is the minimum drug concentration at steady state. This is the drug concentration right before drug administration at steady state.