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Mats Karlsson wrote:
> Those interested in real problems can stop reading here!
>
> Usually we model rate constants (ka, keo, kout, ...) with exponential
> models (ka=THETA(.)*EXP(ETA(.))). Is there any reason to believe that
> this should be better than modelling the corresponding half-lives or
> transit/residence times instead (e.g. MAT=THETA(.)*EXP(ETA(.))? I
> usually find it easier to keep track of how reasonable parameters are on
> the time rather than inverse time scale, so the time scale would in that
> respect to prefer.
I have not been using rate constants in population analyses for a
long time now. I have been using Tabs (absorption half-life), and Teq
(equilibration aka "effect compartment" half lives) instead of KA and
Keq (aka Keo) for the same reason Mats mentions. It is easier for my
(limited) brain capacity to understand parameters which have units of
time rather than 1/time.
The only downside is that somewhere in the code I have to add this:
IF (NEWIND.LE.1) LN2=LOG(2) ; for computational efficiency
and then, for instance, to keep PREDPP ADVAN2 happy:
TABS=THETA(PopTabs)*EXP(etaTabs)
KA=LN2/TABS
As for the suggestion that we consider the population model for Mats :
MATS=THETA(PopMats)*EXP(etaMats)
I think that we should be grateful that Mats is an individual and not
a population :-)
Nick
--
Nick Holford, Divn Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
email:n.holford.at.auckland.ac.nz tel:+64(9)373-7599x6730 fax:373-7556
http://www.phm.auckland.ac.nz/Staff/NHolford/nholford.htm
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)