st: Re: calculation of area under curve with Stata

["Seed, Paul" <paul.seed@kcl.ac.uk>]

Elmir Omerovic wrote:

I am analysing the blood pressure (BP) levels from the three different
groups of animals. BP was measured repeatedly in every animal at 10
different time points within 90 minutes from the start of the experiment.
The animals were exposed to 3 different drugs (each group n=8).

I understand that one way to compare the effect of the drugs on blood
pressure within the whole experimental period would be to calculate the area
under the curve and to use this value in a linear mixed model. 

I would be very grateful if someone could help me with step-by-step
instructions how to calculate AUC in Stata.

************************************************************
AUC is one option for summarising the data, but there are others.  
Peak blood pressure is worth considering. 

In a clinical setting, peak blood pressure is often regarded as more important than mean 
blood pressure; and there is a case for analysing data from animal studies as you would 
a human study..

The command -findit auc- will reveal a number of built-in Stata commands that 
will produce AUC & related pharmacokinetic measures.  
The most useful for measuring blood pressure are auc, cmax and possibly tomax
The full list includes several that make no sense for blood pressure.

    auc                 area under the concentration-time curve (AUC)
    aucline             area under the concentration-time curve from 0 to infinity using a linear extension
    aucexp              area under the concentration-time curve from 0 to infinity using an exponential extension
    auclog              area under the log-concentration-time curve extended with a linear fit
    half                half-life of the drug
    ke                  elimination rate
    cmax                maximum concentration
    tmax                time at last concentration
    tomc                time of maximum concentration



Paul T Seed, Senior Lecturer in Medical Statistics, 
Division of Women's Health, King's College London
Women's Health Academic Centre, King's Health Partners 
(+44) (0) 20 7188 3642.


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