RE: Translate ALAG1 and D1 in ADVAN2 to differential equations
Shelley,
You would use ADVAN6, ADVAN8, or ADVAN13, and code the differential equations
explicitly in the $DES block. See the included CONTROL7 in the NONMEM examples.
Also note, you have an interesting error structure. Usually I have lognormal
errors, that is
KA = THETA(x)*EXP(ETA(x))
You have mu-referenced your variables. When I do this, the following code is
produced:
MU_x = LOG(THETA(x))
KA = EXP(MU_x+ETA(x))
You have instead:
MU_x = THETA(x)
KA = EXP(MU_x+ETA(x))
This means your KA, (which I will call KAs), is equivalent to my KA by the
following transformation:
KAs = LOG(KA)
Is this what you mean?
Matt.
Quoted reply history
From: [email protected] [mailto:[email protected]] On
Behalf Of Xiao Hu
Sent: Tuesday, August 10, 2010 10:50 AM
To: nmusers
Subject: [NMusers] Translate ALAG1 and D1 in ADVAN2 to differential equations
Dear NMusers,
I'm using ADVAN2 to model the PK of a drug. To best fit the profile, the model
includes ALAG1 and D1. For the next step, the ADVAN2 needs to be translated
into differential equation to include a PD compartment. How should I write the
differential equation for ALAG1 and D1? As you can see, there is Ka in the
ADVAN2 model. I'm not very clear what's the meaning of D1 and KA when both are
modeled. Any hint or previous link would be appreciated. Thanks in advance!
$SUBROUTINES ADVAN2
$PK
KASC=THETA(4)
VSC=THETA(5)
CLSC=THETA(6)
LGSC=THETA(8)
MU_4=KASC
MU_5=VSC
MU_6=CLSC
MU_8=THETA(11)
SD=THETA(9)
SIG=SD
KA=EXP(MU_4+ETA(4))
V=EXP(MU_5+ETA(5))
CL=EXP(MU_6+ETA(6))
K=CL/V
S2=V/1000; DOSE IN 1000 U, CONC in U, VOLUME IN mL
ALAG1=LGSC*EXP(ETA(10))
D1=EXP(MU_8+ETA(8))
Final parameter estimates:
$THETA
12 ;THETA5
8.89 ;THETA6
0.0015;THETA8
0.263 ; THETA9
2.87; THETA11
Best regards,
Shelley
========================================
Xiao Hu (Shelley), Ph.D.
Scientist,
Development Pharmacokinetics & Disposition
Biogen Idec, Inc.
14 Cambridge Center
Cambridge, MA 02142
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