- On 10 Apr 2001 at 13:35:37, Amir Abbas Tahami Monfared (tahamima.aaa.MAGELLAN.UMontreal.CA) sent the message

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Dear NONMEM users,

I used NONMEM to do the population modeling and I have a couple of

questions. The data items are specified for the following single-dose

infusion type (Inf. time=2). I used one and two-cmt models. The results

and the goodness of fit satisfies the use of two-cmt model. However, I

noticed that the estimate of VSS (VSS=theta(4)+eta(4)) for all

individual is identical after POSTHOC estimation.

zero order infusion with inf.time=2, data for one individual:

Sub. Dose Time DV RATE

1 100 0 0 50

1 . 0 0 .

1 . 1 3.22 .

1 . 2 3.55 .

1 . 2.1 2.72 .

1 . 2.3 2.42 .

1 . 2.5 1.86 .

1 . 3 1.40 .

1 . 4 0.45 .

1 . 5 0.53 .

1 . 8 0.32 .

I tried this control stream:

$PROB Population PK ...

$INPUT ID AMT TIME DV RATE

$DATA Data

$SUBS ADVAN3 TRANS3

$PK

TVCL=THETA(1)

CL=TVCL+ETA(1)

TVV=THETA(2)

V=TVV+ETA(2)

TVQ=THETA(3)

Q=TVQ+ETA(3)

TVVSS=THETA(4)

VSS=TVVSS+ETA(4)

S1=V

$ERROR

Y=F+ERR(1)

$THETA

(0.1,30)

(0.1,25)

(0.1,50)

(0.1,100)

$OMEGA 0.25 0.25 0.25 0.25

$SIGMA 0.04

$EST SIGDIGITS=4 MAXEVAL=999 POSTHOC PRINT=5

$COV

$TABLE ID TIME CL V Q VSS

$SCAT TIME VS DV

$SCAT ...

I would also like to add that the estimates for volume of distribution

in central cmt. and VSS are half of the mean estimate obtained by STS

method.

If someone has any advice, comments, on the above specification, or

suggestions for how to model such data, I would really appreciate it.

Thanks in advance.

Amir A. Tahami

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