
78 Computational Pharmacokinetics
Here the elimination term should actually be CL
int
C
u,T
, where C
u,T
is the free
drug concentration in the tissue, but we have assumed this to be in equilibrium
with the free concentration in the outgoing vessel, which is f
u
C
out
.
Assuming a constant CL
int
, and if we apply a continuous infusion on the
ingoing vessel, equation 4.6 implies that we in steady state will get the balance
equation
QC
out
= QC
in
− CL
int
f
u
C
out
,
from which we get the extraction ratio of the organ as
E =
f
u
CL
int
Q + f
u
CL
int
. (4.7)
It follows that the total blood clearance of the organ can be computed from
CL
org
= Q · E =
Qf
u
CL
int
Q + f
u
CL
int
.
The importance