RE: Fx

From Nick Holford Subject: RE: [NMusers] Fx Date: 5/24/2004 5:01 PM Paul, F2 is the bioavailability of AMT (specified in the data file) into CMT 2. It is not the fraction of drug moving from depot (CMT=1) to central (CMT=2). For your oral dosing data set you can only meaningfully apply F1 to describe bioavailability from the depot. I don't recommend using V2 in the $DES. The DADT means dAMT/time so stick to thinking in amount not conc for these equations. Finally, you need to be aware of identifiability issues. Given oral drug you cannot estimate F1 (but you can estimate between subject variability in F1). Similary you cannot estimate V3 (metabolite volume) without assuming all the parent goes to the metabolite. Usual thing to do is to assume all clearance goes to metabolite and forget about trying to distinguish CL from CLM or you can assume and FIX V3 to some plausible value e.g. same as V2. Then you can distinguish CL from CLM. Nick -- Nick Holford, Dept Pharmacology & Clinical Pharmacology University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand email:n.holford@auckland.ac.nz tel:+64(9)373-7599x86730 fax:373-7556 http://www.health.auckland.ac.nz/pharmacology/staff/nholford/