Dear Friederike,
Please, step back for one minute and try to understand what you want to find out: You are applying a nonlinear mixed-effects modelling program to obtain parameter values for your model. All parameters in your model are random variables. Some have a mean of zero (ETAs, EPSs) some should have a mean <> 0 (THETAs). Your results are not point estimates but distributions. Therefore you should approach the question of Cmin and Tmin through simulation and report the confidence interval (or other stats) for your parameters of interest. Thus construct a simulation data set with dense time points around the expected Tmin, and run $SIMULATION (240311) ONLYSIMULATION SUBPROBLEMS=1000 $TABLE ID TIME ...... NOHEADER NOAPPEND NOPRINT FILE=xxxx.tab with all your final parameter estimates as initial values in your control file. Then analyse your 100 (or 1000) simulated data files with R or SAS and report the distribution of the Cmin and Tmin you found. Please, come back with more questions in case I have confused you, Joachim Joachim Grevel, PhD Scientific Director BAST Inc Limited BioCity Nottingham Pennyfoot Street Nottingham, NG1 1GF Tel: +44 (0)115 8120497 From: [email protected] [mailto:[email protected]] On Behalf Of Friederike Kanefendt Sent: 06 April 2011 09:56 To: [email protected] Subject: [NMusers] Modeling Cmin and Tmin Dear NMUser, I am a beginner in NONMEM and I have a question regarding modeling Cmin and Tmin. I have data of a biomarker which decreases after drug intake and I want to determine the minimum change from baseline (Cmin) as well as the corresponding time (Tmin). I tried different models but the estimated values for these parameters are not plausible or always zero. Has someone experience with this or any idea to solve this problem? Thanks a lot Best regards Friederike Attached I send you a part of my code: $SUBROUTINE ADVAN6 TOL=3 ... $DES ... DADT(5) = KIN*INH-KOUT*A(5) ; Biomarker CMT IF(TIME.EQ.0) THEN CMIN = BASE ; Baseline conc also estimated by NM TMIN=0 ENDIF CC=A(5) IF(CC.LT.CMIN) THEN CMIN= CC TMIN= T ENDIF REL = CMIN/BASE ; change relative to baseline ... $ESTIMATION SIG=2 PRINT=1 METHOD=1 INTER MAXEVAL=0 NOABORT Friederike Kanefendt Pharmacist, PhD-Student University of Bonn -Clinical Pharmacy- An der Immenburg 4 D-53121 Bonn Phone: +49 (0)228 73-5781 Fax: +49(0) 228 73-9757 [email protected]
