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 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.