Repetitive Extravascular Dosing

Cmin and Cmax can also be calculated if the drug is administered via an extravascular route.  The equations however become more complex.  From an equation describing the plasma concentration versus time curve after one extravascular administration(@), our new equation may be written as follows:

where D is the dose administered and F is the fraction of the dosage absorbed.  [FD = DGO]

At certain fixed intervals(T), n doses of the drug are administered and so the plasma concentrations following the nth dose are obtained by

where t' is the time elapsed after the nth dose.  When n is large (as when the plasma [ ] reach a plateau), the terms exp(-nkelT) and exp(-nkaT) become neglibly small and so the equation simplifies to