This page allows viewing of a multidose pharmacokinetics
profile from immediate-release (IR) and sustained-release
To use enter the following parameters:
IR Dose: This is
amount of the immediate-release portion of the dose. For a
sustained-release product this is normally no more than
half the total
IR t 1/2 abs: This is the absorption half-life for the immediate-release portion of the dose, usually about 0.5 to 1.0 hours. The absorption rate, ka, is related to the half-life by ka = ln(2)/(t 1/2 abs).
SR Dose: This
is the amount of the sustained-release portion of the
dose. This is
generally more than half the total dose.
t 1/2 abs: This is the absorption half-life for the sustained-release portion of the dose, usually about 2 to 3 hours. The absorption rate, ka, is related to the half-life by ka = ln(2)/(t 1/2 abs).
time interval between doses. Generally a
dose interval is chosen to be approximately equal to the
If you want to see what a single, non-repeating dose looks
the Dose Interval to a ridiculously large number, say
Duration: This is
duration of the pharmacokinetics profile that
will be displayed.
t 1/2 elim: This
elimination half-life. The elimination rate, ke, is
related to the
half-life by ke = ln(2)/(t 1/2 elim). Because of a quirk
mathematics, don't set the absorption and elimination
to each other. When determining ke and ka from blood data,
horrible called flip-flop kinetics occurs if ke is greater
than ka. But
that horribleness does not carry over to this calculation,
Vd: This is the
distribution. You only need to know this if you want exact
f: This is the
drug absorbed or the bioavailability. You only need to
know this if you
want exact values for blood levels.
After you hit the Replot! button, the PK profile is
the text of the data is inserted into the text box. The
text starts off
with a rehash of the input data and includes calculation
of ka, ke and
clearance. The Clearance
calculated as the product of ke and Vd.
The text then provides values resulting from the first
Lastly, the time (t)
blood level (Cp)
given. These data may be copied and pasted into an Excel
spreadsheet for better control over graphing, or for
multiple curves on the same graph.
Here are two examples comparing multidose
profiles. In the first example, a 4-hour IR dose with an
absorption half-life is compared to an 8-hour SR dose with
absorption half-life. For both the elimination half-life
is 4 hrs.
In the second example, three curves have been generated
which the dosage is either all IR, all SR or an even split
two. The parameters are the same as the first example,
except that all
dosing is done in an 8-hour interval.
by Jeffrey Clymer. Email.
Debut: April 14, 2009. Revision No. 1.