Parameterization!!!

From: "Sreenivasa Rao Vanapalli" <svanapal@blue.weeg.uiowa.edu> Subject: Parameterization!!! Date: Tue, 8 May 2001 16:51:26 -0500 Hello NMUsers I have data obtained after oral administration and trying to fit to a two compartment model with NONMEM. I know that the data fit to two comaprtment. Intitially I fitted the data with WinNonlin and now trying population compartmental model. When I tried with microconstants (KA, K12, K21, K, Vd) I could compare these estimates with WinNonlin values. But with clearance parameters, the estimates are quite different. The estimate for central compartment with clearance parameter (ADVAN4 TRANS4) was only 0.5 liters. Where as VD estimate with microconstant parameters (ADVAN4)was 13 liters. Same case with KA also. Can some one explain why this is happening? Regards Sreenivasa Rao Vanapalli, Ph.D, Janssen Postdoctoral Research Scholar, S411 PHAR, College of Pharmacy, University of Iowa, Iowa City, IA-52242 319-353-5157 (Office) 319-337-2687 (Home)