On 28 July 2010 16:54, Jan-Stefan Van der Walt < janstefan.vanderw...@gmail.com> wrote:
> Dear Matt, > > In my experience, using ADVAN13 (NONMEM7) reduces the estimation time for > the transit compartment model. Also, you can use DOSTIM to capture the time > of doses specified using the ADDL data item when using the analytical > solution published by Savic et al. > > Regards from Uppsala, > Jan-Stefan > > > > On 17 July 2010 07:59, Justin Wilkins <justin...@gmail.com> wrote: > >> Dear Matt, >> >> We published a multiple-dose implementation of the transit model a little >> while back which may be of help (although it uses the mathematical solution >> from Savic et al 2007, and assumes the entire bioavailable dose has left the >> absorption compartment before the next dose is given). I'm not sure that >> hard-coding the number of compartments as you suggest is an easier solution, >> though, given the time it might take to empirically (?) narrow down the >> number of transit compartments you need, and the computational overhead of >> using so many differential equations. Why did you choose 25 as a starting >> point, incidentally? >> >> We had similar experiences (numerical instability under some >> circumstances) in our own implementation of the Stirling approximation to >> the gamma function in NONMEM VI. >> >> Wilkins JJ, Savic RM, Karlsson MO, Langdon G, McIlleron H, Pillai G, Smith >> PJ, Simonsson US. Antimicrob Agents Chemother. 2008 Jun;52(6):2138-48. >> Savic RM, Jonker DM, Kerbusch T, Karlsson MO. J Pharmacokinet Pharmacodyn. >> 2007 Oct;34(5):711-26 >> >> Best >> Justin >> >> On 16 July 2010 18:00, Zierhut, Matt <matt.zier...@amylin.com> wrote: >> >>> All, >>> Has anyone ever used a transit compartment model in NONMEM for PK with >>> multiple doses. We are looking to use ~25 transit compartments (and thus >>> ~25 DiffEqs in the $DES block). This seems easier for multiple doses, >>> compared to the mathematical solution detailed in Rada Savic's 2004 PAGE >>> presentation. We are also trying to implement the gamma scaling factor in >>> the transit compartment equations (Sun YN, Jusko WJ. J Pharm Sci. 1998 >>> Jun;87(6):732-7), but it seems to be fairly unstable in NONMEM. Can >>> anyone comment/help? >>> >>> Thanks in advance, >>> Matt >>> >> >> >> >> -- >> Justin Wilkins >> ----------------------------- >> Colmarerstrasse 31 >> 4055 Basel >> Switzerland >> ----------------------------- >> Email: justin...@gmail.com >> Skype: kestrel_za2002 >> Mobile: +41 76 561 0949 >> >> > > > -- > /Jan-Stefan > -- /Jan-Stefan
