NONMEM Users Network Archive

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Re: lagged absorption and empirical input function

From: Luann Phillips <Luann.Phillips>
Date: Wed, 27 Jul 2011 22:01:10 -0400

Pierre-Olivier,

NONMEM takes care of all inputs via the structure of dosing records in
the input dataset. Therefore, they are not included in the $DES block.

Instead:

In the input dataset

ID TIME AMT DV etc.
1 0 100 .
1 1 . 5
etc.


$PK
ALAG1=THETA(#) ;this will be the estimate of the absorption lag
S1=1/V
etc.

$DES
;note NONMEM codes diff. eqs. in amount units. The scale parameter (S1)
;in $PK is used to convert the amount (AMT) unit to the DV (or conc.)
;unit
;NONMEM will insert the dose of 100 at the TIME of the dose in the
;dataset + ALAG1. The input will remain zero until that time automatically.

DADT(1)=-K*A(1)

----------------

If you are fitting a basic 1 cmt model with first-order elimination, I
would recommend using subroutine ADVAN1 TRANS1. You don't provide $DES
for this model. You just supply $PK.

$PK
K=THETA(1)
V=THETA(2)
ALAG1=THETA(3)
S1=1/V ;or whatever is appropriate for your units of dose,v,and dv.


-------------

Best Regards,

Luann Phillips
Director, PK/PD
Cognigen Corporation


Tremblay, Pierre-Olivier wrote:
> Hi,
>
> I'm trying to implement an absorption lag-time into a model described by
> differential equations and using an empirical input function.
>
> My initial idea was to define a MTIME(1) corresponding to the lag-time
> and to use MPAST(1) to set the start of the input as below.
>
> DADT(1)=(DOSE/V)*INPUT*MPAST(1)-K*A(1)
>
> However, I only end up with no input at all in the system resulting in
> simulated DV of 0 residual error. The issue seems related to the use
> MPAST with the input function but I don't know how.
>
> Would anyone be kind enough to point me in the right direction?
>
> Thanks,
>
> Pierre-Olivier
>
Received on Wed Jul 27 2011 - 22:01:10 EDT

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