Re:
Susan,
In my experience very large estimates for volume of distribution are almost
always a results of inaccuracies with units between concentration observations
(DV), dosing amounts (AMT), and the scale parameter (S). I believe you can
correct your issue by adjusting the S2=V code in your control stream. Please
see my blog (blog.learnpkpd.com) for a complete description. The specific post
on the scale parameter is located here: http://wp.me/p1fZzZ-4O
Best of luck!
Nathan
_____________________________
Nathan Teuscher
Founder
PK/PD Associates
[email protected]
www.learnpkpd.com
blog.learnpkpd.com
www.youtube.com/learnpkpd
www.twitter.com/learnpkpd
Quoted reply history
On Mar 5, 2011, at 11:02 AM, Susan Al taher wrote:
> Hi
>
> I am trying to build a structural model for an oral drug. I am getting
> extremely large and unreasonable values for vd, eg a billion L, putting an
> upper limit on theta will give a near boundary warning.
>
> Does anyone have an idea why this might occur and how to solve it.
>
> This is part of the input file:
> $SUBROUTINE ADVAN2 TRANS2
> $PK
> TVCL = THETA(1)
> CL = TVCL*EXP(ETA(1))
> V = THETA(2)
> KA = THETA(3)
> S2 = V
>
>
> $THETA (0,10)
> $THETA (0,20)
> $THETA 2 FIXED
>
>
> Best regards
> Susan