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 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
