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Re: [NMusers] Why should we avoid using micro rate constants?

From: Bonate, Peter <>
Date: Sun, 3 Feb 2019 22:37:45 +0000

You may have found a local minima with the microconstant parameterization.

There generally isn’t any rhyme or reason for why one chooses macro or micro constants. People will argue that the macro model with Q and Vp is more interpretable than k12 and k21. That, and scaling reasons, are why one might choose one parameterization over another.

Pete Bonate

On Feb 3, 2019, at 2:54 PM, Singla, Sumeet K <<>> wrote:

Hello everyone!

I have a question. I was trying to build a 2-compartment PK model for marijuana use in occasional and chronic smokers. Initially, I was using providing rate constants K12 and K21 ­in PK block and it resulted in poor fitting. Then, I later changed to CL,V1, V2 , Q and it resulted in proper fitting. I was perplexed as to why I couldn’t get a proper fit by providing rate constants? I tried to look online but couldn’t find any proper explanation about when (or not) we should use micro constants in PK block to define our model in NONMEM? Does anyone has any useful insights into this?

Sumeet Singla
Graduate Student
Dpt. of Pharmaceutics & Translational Therapeutics
College of Pharmacy- University of Iowa

Received on Sun Feb 03 2019 - 17:37:45 EST

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