RE: [Fwd: occasions during pregnancy]
Hi Paul,
When you treat each occasion as a different patient you get
subject-by-occasion specific predictions of all the parameters in your model
(or at least for those parameters in which you include an IIV eta)...not
just clearance. Thus, it is not surprising that you might get a better fit
by doing this relative to your code below. If IOV>IIV on your other
parameters you might consider evaluating IOV on other parameters in addition
to CL. If your model is for PO dosing, you might also consider putting IOV
on a relative F parameter as often differences in apparent CL/F and apparent
V/F between occasions is often due to differences in absorption between
occasion rather than due to differences in the disposition kinetics for CL
and V.
Ken
Quoted reply history
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of [email protected]
Sent: Tuesday, March 01, 2011 10:53 AM
To: nm nm
Subject: [NMusers] [Fwd: occasions during pregnancy]
---------------------------- Original Message ----------------------------
Subject: occasions during pregnancy
From: [email protected]
Date: Tue, March 1, 2011 10:49 am
To: "nm nm" <[email protected]>
--------------------------------------------------------------------------
Hi all nmusers,
I thank all who responded my questions yesterday. Almost all the responses
suggested that several occasions of one patient should be put under one ID
#. I re-code my control stream and adjusted the data file as following:
$PK
K12 = THETA(1)*EXP(ETA(1))
CL=
THETA(2)*EXP(ETA(2)+ETA(6)*TRI1+ETA(7)*TRI2+ETA(8)*TRI3+ETA(9)*TRI4)
$OMEGA
.8;
.1 .8;
.1 .1 .8;
.1 .1 .1 .8;
.1 .1 .1 .1 .8;
$OMEGA BLOCK(1) 0.9;
$OMEGA BLOCK(1) SAME;
$OMEGA BLOCK(1) SAME;
$OMEGA BLOCK(1) SAME;
where TRI1,TRI2,TRI3, and TRI4 are different stages of pregnancy.
This model fits poorly for the data (from the plot of PRED, IPRED VS. DV),
although the estimates are stable and reasonable.
If I treat the different occasions as different patients, ignoring the
correlation within the same patients, then the model fits quite well and
the results are reasonable.
I also noticed one note from Lewis Sheiner:
Note that, as happens more often, at least with human data, than one might
have thought, the IOV>IIV, then treating each occaasion as though it were
a distinct individual is a reasonable approximation.
--------------Date: Wed, 17 Nov 1999 13:57:18 -0800
From: Lewis Sheiner <[email protected]>
Subject: Re: repeating cases---------
The parameters during pregnancy change quite large, so I am not sure if it
is a reasonalble approximation to treat occasions as distinct individual,
or I have to search the better models of putting those occasions under one
ID? and what is the direction to improve the model?
Any suggestion is greatly appreciated.
Paul
School of Pharmacy
University of Pittsburgh
716 Salk Hall
3501 Terrace Street
Pittsburgh, PA 15261
Phone: 412-648-8546
E-mail: [email protected]
Yuanyue (Paul) Gao
School of Pharmacy
University of Pittsburgh
716 Salk Hall
3501 Terrace Street
Pittsburgh, PA 15261
Phone: 412-648-8546
E-mail: [email protected]