I’ve got a vanilla dataset: orally-dosed mouse, two dose levels (20, 40 mg/kg), 8 timepoints, n=3 at each point. Trying to fit a PK model to the data. In a Classic model, I can specify that the dose is 20 mg, then select from the Normalization drop-down menu so that it reads ‘kg’. Then I know that the normalization will be carried through the analysis, and my V_F will have units of mL/kg. So far so good. I love the interface to the Phoenix models, especially the Initial Estimates tab. However, I can’t for the life of me find where to tell it that my doses should be normalized. Fitting proceeds without problems, and visually looks great. But my volume parameter comes out with no units at all, and is 10-20 fold smaller than the Classic model. Now, although it looks OK visually, my CV is horrible in the Classic model (Phoenix has better CV), so I’m not too worried about the numerical discrepancies (for now). I’d just like to know how to dose-normalize. Has anyone figured it out? Do I just take care of it myself (that’s fine)? Anyone else had situations in which Phoenix got a better-quality fit (i.e., lower CV) or worse? Thanks, -Frank
Company firewall ate my previous (carefully crafted) attempt to post, so I’ll keep this one brief: Has anyone figured out how to do dose-normalization in a Phoenix model? In a Classic model, I would just input the dose (in ng or mg), then selection ‘kg’ from the drop-down menu, indicating that my dosing was in mg/kg. Then the units are carried through, and my V_F has units of mL/kg, instead of just mL. I cannot see how to do this in a Phoenix model, and would welcome some pointers. If it can’t be done, that’s fine - I can carry through on my own. It’s just that my volume parameter comes out with no units at all attached, and I’d like to know what’s going on. Thanks, -Frank