# [NMusers] RE: Dataset coding for baseline endogenous substance

From: Denney, William S. <William.S.Denney_at_pfizer.com>
Date: Tue, 26 May 2015 23:01:41 +0000

Generally, you will just include the baseline measurement as time=0 and t=
hen reference all other times from that time. So, if your baseline value w=
as drawn at 8AM on day 1 while the first dose was at 10AM, just set the bas=
eline time as 0 and the first dose time as 2 (also assuming that your time =
is in hours). If baseline is taken far before the next time, the only impo=
rtant part is that you want the time between baseline and the next measurem=
ent to be more than ~5-fold the auto-correlation time of your system.

From there, you will estimate your A_0 values as you have seen other places=
. A general note that is not always covered in other discussions of endoge=
nous substance PK: You want to make sure that your equations work so that =
A_0 is at steady state (usually). Often, you will not directly set A_0, bu=
t you will solve the equations for A_0 being steady-state and set it to the=

Thanks,

Bill

From: owner-nmusers_at_globomaxnm.com [mailto:owner-nmusers_at_globomaxnm.com] On=
Sent: Tuesday, May 26, 2015 6:02 PM
To: nmusers_at_globomaxnm.com
Subject: [NMusers] Dataset coding for baseline endogenous substance

I am modeling a drug that is also an endogenous substance.

I have found quite a bit of information on modeling practices with endogeno=
us substances, but nothing on how to incorporate the baseline endogenous su=
bstance value (DV) into the dataset.

The data is from clinical use, and the baseline values are not drawn at exa=
ctly the same times prior to drug administration.

Any assistance would be appreciated! Thank you in advance...

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