# Re: Modelling IV and IP simultaneously

From: Leonid Gibiansky <lgibiansky>
Date: Mon, 24 Apr 2017 12:00:00 -0400

CMT is important for dosing: it directs the dose to the appropriate
compartment (equation number).

It is a common misconception that CMT has to be related to observations.
It is relevant for observations only if F notation is used (and
therefore it is better to avoid using this notation).
For observations, one can set any compartment number (within the range
from 1 up to the number of equations in the model). Then, a separate
variable TYPE can be used, for example:

Y=A(2) + error ; for parent (TYPE=1)
IF(TYPE.EQ.2) Y = A(6)+A(7)+A(8) + error ; for metabolite (TYPE=2)

In this case, compartment number found on observation records can be
ignored. It will direct NONMEM to set F to the A(CMT) value, but if F is
not used, then it has no effect on the model or results.

Leonid

On 4/24/2017 11:26 AM, Fanny Gallais wrote:
> Dear NMusers,
>
>
>
> I'm having trouble writing the code for my model. I have IV and IP
> administrations data, that I would like to model simultaneously. We
> found out that IP was best modeled by a first order absorption, using an
> input compartment (DADT(1)=-KA*A(1)). At first, we used a CMT column in
> the dataset to indicate for each dosing event if it is IV or IP. But
> then, as we made the model more complicated, we realized that we
> couldn't use a CMT column. We study the parent compound, as well as its
> metabolite at the same time but the problem is we cannot put a
> compartment number for the metabolite's observations. This is because,
> given the model structure, the prediction for the metabolite
> concentrations is a sum of 3 concentrations in 3 different compartments
> (e.g. IPRED=A(6)+A(7)+A(8)). So we think that putting a compartment
> number for the observation would be confusing for NONMEM. What do you
> think? Do you see how we could model IV and IP simultaneously, without
> using the CMT column ? or any other solution?
>
>
>
> Thank you for your help
>
> Fanny Gallais
Received on Mon Apr 24 2017 - 12:00:00 EDT

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