This page allows viewing of a multidose pharmacokinetics
To use enter the following parameters:
loading dose of zero. A suggested
loading dose will be given in the results text field. The
value of the
Loading Dose is added to the Repeating Dose for the value
of the total
dose given at each
interval, including the first dose.
If you want to examine a single dose, set the Loading Dose
keep this as the single dose and set the Dose Interval to
ridiculously large number.
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 abs: This
absorption half-life. For an immediate release dosage
absorption half-life is usually about 0.5 to 1.0 hours.
release dosage forms, the absorption half-life may be
about 2 to 3
hours. The absorption rate, ka, is related to the
half-life by ka =
ln(2)/(t 1/2 abs). To mimic an intravenous bolus dose, set
the t 1/2
abs to a very small number, say 0.001 hr. To mimic
set the t 1/2 abs to a very low number and set the Dose
Interval to a
similarly small number.
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
does not include the Loading Dose, just the amount in the
The next part gives the long-term steady-state values.
The Suggested Loading
is that amount which when added to the Repeating Dose
initial peak up to the steady state level. Again, the
Loading Dose in
this calculation is the amount added to the Repeating Dose
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's an example comparing a multidose pharmacokinetics profile with and without a loading dose.
by Jeffrey Clymer. Email.
Debut: April 2, 2009. Revision No. 1.