RE: VD as a fraction of another VD
Hi Orlando,
This is somewhat dependent on how exactly you want the fraction to be coded.
Most likely, you want to restrict the volume to be positive and not bounded
between 0 and 1 (i.e. it is ≥0). Given that, you can define V3 as:
V3=EXP(THETA(8))*V1
You would then just exponentiate THETA(8) to find the fraction.
You can separately estimate the volume using the same ETA as the parent central
volume as:
V3=THETA(8)*EXP(ETA(1))
That way, it won’t explicitly be a fraction of the parent, and that may lead to
a more stable model.
Thanks,
Bill
Quoted reply history
From: [email protected] [mailto:[email protected]] On
Behalf Of Carlos Orlando Jacobo Cabral
Sent: Monday, May 21, 2012 2:19 PM
To: nonmem users
Subject: [NMusers] VD as a fraction of another VD
Dear NMusers,
Hi, I have data of a parent drug (intravenously administered) and its
metabolite, ¿How can I code the volume of distribution of metabolite as a
fraction of the central volume of parent?
An example of the model that I want to fit is:
$PK
V1=THETA(1)*EXP(ETA(1)) ; Central Volume of parent
V2=THETA(2)*EXP(ETA(2)) ; Peripheral Volume of parent
Q=THETA(3) ; intercompartmental clearance
V3= ???????????? ; Volume of metabolite as a fraction of V1 with variability
CL1=THETA(5)*EXP(ETA(4)) ; Formation clearance of metabolite
CL2=THETA(6)*EXP(ETA(5)) ; Elimination clearance of metabolite
CL0=THETA(7)*EXP(ETA(6)) ; Parent drug excretion by routes other than formation
of metabolite
- Thank you in advance.
Orlando.
PhD student Carlos Orlando Jacobo Cabral
Departamento de Farmacología, Lab.34
Centro de Investigación y de Estudios Avanzados del I. P. N.
Email: [email protected]<mailto:[email protected]>;
[email protected]<mailto:[email protected]>