Dear Sam and others,
I prefer to be a lurker on this email list. I'd rather
not be drawn into a lengthy discussion ...!
To answer your question, it might look something like this:
$PK (NON-EVENT)
MTIME(1)=THETA(8) ; start of change due to meal #1
MTIME(2)=MTIME(1)+THETA(9) ; end of change due to meal #1
MTIME(3)=THETA(10) ; start of change due to meal #2
MTIME(4)=MTIME(3)+THETA(11) ; end of change due to meal #2
....
$DES
FLAG1=MPAST(1)-MPAST(2) ; =1 only between MTIME(1) and MTIME(2)
FLAG2=MPAST(3)-MPAST(4) ; =1 only between MTIME(3) and MTIME(4)
FLAG=FLAG1+FLAG2
DADT(1)=-KA*A(1)+K41*A(4)*FLAG
DADT(4)=K1G*A(2)-K41*A(4)*FLAG
(or perhaps
DADT(1)=-KA*A(1)+K41*A(4)*FLAG1+ a different term *FLAG2
DADT(4)=K1G*A(2)-K41*A(4)*FLAG1- a different term *FLAG2
if something different happens the second time period)
You will have to be careful to constrain the thetas so that the
intervals do not overlap.
Another way to do it:
NM-TRAN allows MTIME to be changed.
Here, there are 3 EHC events. Its a very simple model,
assumes the same length of time for each,
and known time between events.
Constants like 4 and 6 can of course be modelled
and different lengths of time for the EHC events can be modelled
$PK (NON-EVENT)
STIME1=THETA(8)
STIME2=STIME1+4
STIME3=STIME2+6
MTIME(1)=STIME1
IF (TIME.GE.STIME2) MTIME(1)=STIME2
IF (TIME.GE.STIME3) MTIME(1)=STIME3
MTIME(2)=MTIME(1)+THETA(9)
....
(no change to $DES block)
There are *lots* of ways this can be done. I hope this gives you a
reasonable start.
Id' rather someone in the nmusers group work out the details with real
data, and let the others know, so that I can bow out of this thread and
resume lurking.
On Thu, 04 Dec 2008 14:06:27 -0500, "Sam Liao"
<[EMAIL PROTECTED]> said:
> Dear Alison:
> Thanks for let us know this new feature in nm 6. I have been working on
> EHC modeling for single dose as well as multiple dose pk data. I have
> some questions on how to use this new feature.
> How do we define the FLAG when we also have MTIME(3), MTIME(4), MTIME(5)
> and MTIME(6)? We observed one peak after each meals and there were
> three meals each day.
>
> Best regards,
> Sam Liao
> Pharmax Research
> > Dear Sam and Ayyappa,
> >
> > The postings that Sam mentioned are obsolete.
> > The first of the model time examples ("help mtime") suggests a
> > better technique for modelling EHC using MTIME parameters, as follows:
> >
> > Enterohepatic Recycling
> >
> > This fragment of abbreviated code may be used to model EHC. The
> > transfer of drug from compt. 4 to 1 is controlled by FLAG, which
> > is 1 between the times specified by MTIME(1) and MTIME(2), and is
> > 0 otherwise.
> >
> > $PK
> > MTIME(1)=THETA(8)
> > MTIME(2)=MTIME(1)+THETA(9)
> > ....
> > $DES
> > FLAG=MPAST(1)-MPAST(2)
> > DADT(1)=-KA*A(1)+K41*A(4)*FLAG
> > DADT(4)=K1G*A(2)-K41*A(4)*FLAG
> > ....
> >
> > >From "Intro.to NONMEM VI" guide:
> >
> > There is a new feature: model event times. These are additional PK
> > parameters MTIME(i) defined in the PK routine or $PK block. A model
> > event time, like an absorption lag time, defines a time to which the
> > system is advanced, but whose value usually cannot be known in advance.
> > When the time is reached, certain indicator variables are set and a call
> > to PK is made. At this call PK, DES, AES and ERROR can use the indicator
> > variables to change some aspect of the system, e.g., a term in a
> > differential equation, or the rate of an infusion. Thus, a model event
> > time can be used e.g. to mark the time at which the gall bladder begins
> > to empty. A model event time could be implemented by using an absorption
> > lag time, and this is what has been done until now, but doing this is
> > somewhat clumsy. There may be up to PCT model event times, where PCT is
> > a new installation parameter defined in SIZES. Its default value is 30.
> > (See the MTIME and $PK and PRDPK1 and PRDPK2 Help Items and the MODEL
> > TIME Example)
> >
> >
> >
> > On Thu, 04 Dec 2008 08:43:59 -0500, "Sam Liao"
> > <[EMAIL PROTECTED]> said:
> >
> >> Dear Ayyappa:
> >>
> >> I think you will find the following nmusers net post useful for your
> >> model. Alison had kindly provided some code for a EHC model.
> >>
> >> Best regards, Sam Liao Pharmax Research
> >> ===================================================================
> >>
> >> *Enterohepatic Recirculation Model <
> >> http://www.cognigencorp.com/nonmem/nm/98oct061998.html>* *|...
> >> |*this compartment to the change-point. Based on these ideas, here's
> >> how I would modify Rik's code. The change also provides for the
> >> termination of *EHC <
> >> http://www.cognigencorp.com/nonmem/nm/98oct061998.html#pgfId=424161>*.
> >> If you want to let *EHC* continue indefinitely, delete compartment 6
> >> and its dose, and the code involving ALAG6. 1) Add 2 more
> >> compartments to $MODEL:*| ...|* /
> >> http://www.cognigencorp.com/nonmem/nm/98oct061998.html/ 05/06/03,
> >> 19876 bytes
> >>
> >>
> >>
> >>> Dear All,
> >>>
> >>> I am trying to model PK data of a drug and many subjects show double
> >>> peaks but even in fasting state. Can we expect EHC in fasting
> >>> state? Can anybody provide some coding help in modeling intermittent
> >>> episodes of EHC rather than continuous mode?
> >>>
> >>> Thank you.
> >>>
> >>>
> >>> Regards, Ayyappa Chaturvedula
> >>>
>
--
Alison Boeckmann
[EMAIL PROTECTED]
