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# Advanced bio-availability use cases

### Purpose

The bioavailability parameter p, available in the administration macros (‘depot’, ‘absorption’, and ‘iv’), defines the fraction of dose absorbed by the administration type.

The bioavailability parameter can also be used to perform a unit conversion between the amount provided in the data set and the quantities represented in the model (for instance from mg to mmol). For this usage, p can take values greater than 1.

### Example

In the following example, we compare a zero-order absorption process, a first-order absorption process, and a process with mixed zero and first-order absorptions.

<MODEL>
[LONGITUDINAL]
input = {V, Tlag, ka, Tk0, F}

PK:
compartment(cmt=1, amount=A1, concentration=Cc_zoa, volume=V)
absorption(cmt=1, type=1, Tlag, Tk0, p=1)
elimination(cmt=1,k=.25)

compartment(cmt=2, amount=A2, concentration=Cc_foa, volume=V)
absorption(cmt=2, type=1, Tlag, ka, p=1)
elimination(cmt=2,k=.25)

compartment(cmt=3, amount=A3, concentration=Cc_mixed, volume=V)
absorption(cmt=3, type=1, Tlag, Tk0, p=F)
absorption(cmt=3, type=1, Tlag, ka, p=1-F)
elimination(cmt=3,k=.25)

<DESIGN>
[ADMINISTRATION]
adm = {time=5, amount=1, type=1}

<PARAMETER>
V = 10
Tlag = 2
ka = .5
Tk0 = 2
F = .25

<OUTPUT>
grid = 0:.05:20
list = {Cc_zoa Cc_foa, Cc_mixed}

<RESULTS>
[GRAPHICS]
p = {y={Cc_zoa Cc_foa, Cc_mixed}, ylabel='Concentrations', xlabel='Time'}


The zero-order absorption is shown in orange, the first-order absorption in blue and the mixed one in green, in the figure below: 