Chemistry Reference
In-Depth Information
P
app
P
fraction unionised
P
app
65
0.01
P
app
0.65
(b) Before we can calculate the concentration of drug in the
plasma
before
the extraction, we have to consider the concen-
tration present
after
the extraction and remember that all of
the drug in the octanol and the plasma started off in the
plasma. Thus,
concentration in octanol after extraction
P
app
————————------------------
concentration in plasma after extraction
34 ng mL
1
P
app
————----------
plasma concentration
34 ng mL
1
0.65
————----------
plasma concentration
52.3 ng mL
1
To calculate the concentration of drug in the plasma
before
the extraction, we have to convert the concentrations
into amounts (i.e. mass) of drug.
The amount of drug in octanol
after
extraction is
volume
Concentration in plasma after extraction
340 ng
The amount of drug in plasma
after
extraction is
volume
concentration
10
34
261.5 ng
Total amount of drug in the initial plasma sample
concentration
5
52.3
340
601.5 ng
Therefore the
initial
concentration of drug in plasma is
given by
261.5
Amount
601.5
——---
—--
120.3 ng mL
1
Volume
5
(c) The percentage extracted in a single extraction is easily
calculated from the following.
The amount extracted into octanol
340 ng
The total amount of drug in plasma
601.5 ng
Therefore,
