NONMEM Users Network Archive

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Log transformation of concentration

From: Chenguang Wang <maurice.wang>
Date: Thu, 26 Mar 2009 12:15:15 +0100

Dear NONMEM users,

I am working on a PK model and using the log-transformed concentration data.
I'v read some discussions in the NONMEM user group about the log-transformed
concentration. But I am still not very clear about this. Could anybody give
me a reason to do the transform on concentration? Also, I am curious that
after the transform, will the fixed effect have the same meaning as that in
the untransformed model? For example, theta1 is the clearance, after
log-transform of concentration, would the estimation of theta1 still stands
for the population clearance? To my simple thinking about the differential
equation,

d(lnc)/dt= (dc/dt)*(1/c). Therefore, a "c" will be multiplied to the right
term of the orginal differential equation. I think the solution of that
equation might be different from the original one. If it is different, how
can I explain the theta1 in the log transformed model?

Would anyone please give me some explainations or references?

Thanks a lot!

Chenguang

Received on Thu Mar 26 2009 - 07:15:15 EDT

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