RE: Steady state model
Hello Sherwin,
All SS routines source code are located at the C:\nmvi\pr folder.
Each Advan closed form model has specific routines (and equations for SS) that
can be used with it.
For linear models the magic factor for steady state computation will be:
exp(-rate.constant.time)/(1-exp(-rate.constant.Tau).
Monolix guide: Monolix31_PKPD_library.pdf has a lot of SS equations for
commonly used models.
Of course general Advans have their general SS routines too and as Nick
mentioned there is some root finding going on:
a comment from the SS6.FOR routine reads
C SS IS SOLUTION A OF: 0=DADT(A)+R
C APPROXIMATION: DADT(A)=DADT(0)+DA*A
C 0=DADT(0)+DA*A+R
C A=-DAINV*(DADT(0)+R)
...
Happy Reading !
Bests,
Samer
Quoted reply history
-----Original Message-----
From: [email protected] on behalf of Nick Holford
Sent: Wed 8/5/2009 15:44
To: nmusers
Subject: Re: [NMusers] Steady state model
Sherwin,
I dont understand exactly how NONMEM computes the steady state value but
with ODEs it seems to be done using a numerical root finding procedure
i.e. solves for the amt in each of the compartments when all the DEs
have a value of zero.
The amt in each compartment is set to the steady state value. There is
no initial 'parameter' for the compartment. Compartment amounts are
variables. Parameters are constants. Parameters (e.g. THETA values) are
used in the ODEs to define the DE values.
Perhaps Alison Boechmann (who wrote the code) could give a more thorough
answer?
Nick
Sherwin K Sy wrote:
> Dear NONMEM users,
>
> I'm wondering what equation or ODE is used in NONMEM when the steady
> state is set (i.e. SS = 1). Is it the case that the initial parameter
> for the compartment is set to a different value? If so, how does
> NONMEM set this value?
>
> I would appreciate if anyone can provide me with a reference or point
> me to where I can find this information, including the type of
> equation used for extravascular, iv bolus and iv infusion models.
>
> Thanks,
>
> Sherwin
>
>
--
Nick Holford, Professor Clinical Pharmacology
Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
[email protected] tel:+64(9)923-6730 fax:+64(9)373-7090
mobile: +64 21 46 23 53
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford