**[R] pkexamine** -- Calculate pharmacokinetic measures

__Syntax__

**pkexamine** *time concentration* [*if*] [*in*] [**,** *options*]

*options* Description
-------------------------------------------------------------------------
Main
**fit(***#***)** use *#* points to estimate AUC; default is **fit(3)**
__t__**rapezoid** use trapezoidal rule; default is cubic splines
__g__**raph** graph the AUC
**line** graph the linear extension
**log** graph the log extension
**exp(***#***)** plot the exponential fit for the AUC (0 to
infinity)

AUC plot
*cline_options* affect rendition of plotted points connected by
lines
*marker_options* change look of markers (color, size, etc.)
*marker_label_options* add marker labels; change look or position

Add plots
**addplot(***plot***)** add other plots to the generated graph

Y axis, X axis, Titles, Legend, Overall
*twoway_options* any options other than **by()** documented in **[G-3]**
*twoway_options*
-------------------------------------------------------------------------
**by** is allowed; see **[D] by**.

__Menu__

**Statistics > Epidemiology and related > Other > Pharmacokinetic measures**

__Description__

**pkexamine** calculates pharmacokinetic measures from time-and-concentration
subject-level data. **pkexamine** computes and displays the maximum measured
concentration, the time at the maximum measured concentration, the time
of the last measurement, the elimination time, the half-life, and the
area under the concentration-time curve (AUC). Three estimates of the
area under the concentration-time curve from 0 to infinity (AUC) are also
calculated.

**pkexamine** is one of the pk commands. Please read **pk** before reading this
entry.

__Options__

+------+
----+ Main +-------------------------------------------------------------

**fit(***#***)** specifies the number of points, counting back from the last
measurement, to use in fitting the extension to estimate AUC from 0
to infinity. The default is **fit(3)**, or the last three points. This
should be viewed as a minimum; the appropriate number of points will
depend on your data.

**trapezoid** specifies that the trapezoidal rule be used to calculate the
AUC. The default is cubic splines, which give better results for
most functions. When the curve is irregular, **trapezoid** may give
better results.

**graph** tells **pkexamine** to graph the concentration-time curve.

**line** and **log** specify the estimates of the AUC from 0 to infinity to
display when graphing the AUC from 0 to infinity. These options are
ignored, unless they are specified with the **graph** option.

**exp(***#***)** specifies that the exponential fit for the AUC from 0 to infinity
be plotted. You must specify the maximum time value to which you
want to plot the curve, and this time value must be greater than the
maximum time measurement in the data. If you specify 0, the curve
will be plotted to the point at which the linear extension would
cross the *x* axis. This option is not valid with the **line** or **log**
option and is ignored, unless the **graph** option is also specified.

+----------+
----+ AUC plot +---------------------------------------------------------

*cline_options* affect the rendition of the plotted points connected by
lines; see **[G-3]** *cline_options*.

*marker_options* specify the look of markers. This look includes the
marker symbol, the marker size, and its color and outline; see **[G-3]**
*marker_options*.

*marker_label_options* specify if and how the markers are to be labeled;
see **[G-3]** *marker_label_options*.

+-----------+
----+ Add plots +--------------------------------------------------------

**addplot(***plot***)** provides a way to add other plots to the generated graph;
see **[G-3]** *addplot_option*.

+-----------------------------------------+
----+ Y axis, X axis, Titles, Legend, Overall +--------------------------

*twoway_options* are any of the options documented in **[G-3]** *twoway_options*,
excluding **by()**. These include options for titling the graph (see
**[G-3]** *title_options*) and for saving the graph to disk (see **[G-3]**
*saving_option*).

__Examples__

**. webuse auc** (setup)
**. pkexamine time conc** (show measures)
**. pkexamine time conc, fit(7)** (use last 7 point to fit model)
**. pkexamine time conc, trapezoid** (use trapezoidal rule in calculating
AUC)
**. pkexamine time conc, graph** (graph the AUC)

__Stored results__

**pkexamine** stores the following in **r()**:

Scalars
**r(auc)** area under the concentration curve
**r(half)** half-life of the drug
**r(ke)** elimination rate
**r(tmax)** time at last concentration measurement
**r(cmax)** maximum concentration
**r(tomc)** time of maximum concentration
**r(auc_line)** AUC_{0,infinity} estimated with a linear fit
**r(auc_exp)** AUC_{0,infinity} estimated with an exponential fit
**r(auc_ln)** AUC_{0,infinity} estimated with a linear fit of the
natural log