How can we plot regression line to estimate the terminal elimination rate constant?

[P_trivedi]

Hi,

I am performing Noncompartmental Pharmacokinetics in SAS version 9.4 and for that this paper is really very useful.

http://www.lexjansen.com/pharmasug/2005/statisticspharmacokinetics/sp07.pdf 

File required for NCA contains subjectID, Treatment, Time and concentration data.

Generally, terminal elimination constant is calculated from the linear regression of concentration vs. time curve using the least square regression method. For that minimum three points is neded to define the terminal (log-linear) portion of the curve and the selection is based on the best adjusted square coeffiecient of regression (r2).

How can we plot that regression line during the linear phase of the concentration vs. time data to estimate the terminal elimination rate constant (lambda z) using best fit method? How SAS automatically select number of required data points to calculate r2 and draw line to connect that specific points only ?

The desired output has been attached for reference. 

[ballardw]

You will have to provide some guidelines for identifying the points you want. Maybe someone has a solution to something similar to this available but consider this purely fake data plotted below:

Which "linear" bit would you want? Time periods 1-3, 4-7 or 8-10?

[P_trivedi]

Hello all,

     In addition to mentioned query, I would like to elaborate it for better understanding. The point selection (i.e. it can be 3 or more then that) in graph is done automatically using best fit method. So, here the question is how it can be done in SAS? An image of graph has been attached for reference where based on number of data points selected automatically; R2, adjusted r2 and lambda z are calculated.