Re: lagged absorption and empirical input function

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