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
Modelling IV and IP simultaneously
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
Quoted reply history
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