Clearance Models: Noncompartmental Models

Typically, clearance describes the drug elimination from the body using compartment models.

An alternative, the noncompartmental approach, estimates clearance mainly using experimental data collected after a single drug dose.

This approach uses rich sampling data and relates the volume of distribution to systemic exposure and administered dosage, allowing robust clearance computation without any assumptions.

Here, clearance depends on bioavailability, drug dose, and area under the concentration-time curve, or AUC. 

Notably, AUC indicates total systemic exposure after a single dose. Using the trapezoidal rule, first calculate the observed AUC from time zero to t or the last detectable concentration. It is then extrapolated to infinity.

At the steady state, the amount of drug given equals the eliminated amount over that dosing interval, and the clearance equation becomes as follows.

During intravenous infusion's steady state, the clearance formula includes a constant dosing rate and the steady-state concentration, C_ss.