MODELS OF DRUG ADMINISTRATION AND DISPOSITION
In the following image , the effect of drug added via intravenous drug administration is shown by adding a known amount of the drug into the beaker and the graph besides shows the time course of the amount of drug in the beaker.  (CR : Basic and Clinical Pharmacology, Katzung, Lange, 12th Edition)  Example (A):  no movement of drug out of the beaker -->  a steep rise to maximum followed by a plateau.  Example (B): a route of elimination is present --> a slow decay after a sharp rise to a maximum; level of material in the beaker falls --> “pressure” driving the elimination process also falls --> slope of the curve decreases : Exponential decay curve.  Example (C) : drug placed in first "blood" compartment - equilibrates rapidly with second "extravascular" compartment -->  amount of drug in “blood” declines exponentially to a new steady state.  Example (D): model for a more realistic combination of elimination mechanism and extravascu...