NONMEM Users Network Archive

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RE: Your suggestions/thoughts needed on allometric base or final model

From: Bhattaram, Atul <atul.bhattaram>
Date: Fri, 11 Jul 2008 12:57:07 -0400

Hello Hong-Guang


It is always a good idea to estimate the allometric coefficient if you =
have adequate (weight ranges, PK sampling etc) data collected. If body =
weight is not important (although that is rare in pediatrics), then it =
need not be included in the model.




Venkatesh Atul Bhattaram
US Food and Drug Administration

"The contents of this message are mine personally and do not necessarily =
reflect any position of the Government or the Food and Drug =



        From: owner-nmusers
        Sent: Friday, July 11, 2008 12:36 PM
        To: nmusers
        Subject: [NMusers] Your suggestions/thoughts needed on allometric base =
or final model

        Dear NMusers:


        As you know, body weight is an important covariate that is integrated =
into the final or covariate model in some cases. When analyzing =
pediatric pop PK data, body weight-based allometric power model is =
used frequently. By definition, base model is a model without any =
covariates. But, in the literature on the population PK in pediatrics, I =
noted that body weight is added to the structural model (following the =
principles of allometry) before starting the covariate model building in =
some but not in all studies. That means that some models are called =
allometric base models and others are not. What are their differences? =
For the allometric base model, body weight has been added into the base =
model regardless of whether it is an important covariate (in some cases, =
body weight is not). If body weight is not an important covariate as =
determined by further covariate model building, is there still the need =
to add body weight into the final allometric model (if its corresponding =
base model is one without a body weight-associated allometric =
component)? Logically, such a need seems to be not reasonable. How to =
deal with this conflict? Is there an almost agreeable thought on this =
issue in our community?


        Thank you,



Received on Fri Jul 11 2008 - 12:57:07 EDT

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