RE: metabolite modeling

From: "HUTMACHER, MATTHEW" <MATTHEW.HUTMACHER@chi.monsanto.com> Subject: RE: metabolite modeling Date: Thu, 9 Dec 1999 10:35:22 -0600 I am not sure that the model is structurally unidentifiable. If concentration-time data exists for the parent and for the metabolite, all parameters should be unique. My reasoning is as follows: All parameters k12,k23,k32,V1,k20* (k20*=k20+k24) are identifiable in fitting the parent alone with the two compartment model. If one adds in the metabolite, then k24 can be estimated by the conversion portion of the metabolite data so that the parameters k24,V4,k40 should all be identifiable. To set k20=0 will force the conversion rate to be the same as the elimination rate of the parent which I think would induce some lack of fit unless the conversion is 100%. Sequential fitting of the data (fitting the parent first, assessing the fit, if it fits well fixing the parameters for the metabolite fit and then fitting the metabolite) helps me cut down run time for the "getting to know the data" portion of modeling. Especially with complicated models and differing administration routes. Matt