RE: time-controlled drug delivery

From: Nick Holford n.holford@auckland.ac.nz Subject: RE: [NMusers] time-controlled drug delivery Date: Sat, March 20, 2004 5:42 pm Pavel, The variable T represents the current time in the integration interval between two events. TIME is the time at the end of the integration interval. You have written: > $DES > TM=T > RIN=0.1+AMPL*0.1*COS((2*3.14159265/60)*(TIME-60)) > DADT(1)=0.1+AMPL*0.1*COS((2*3.14159265/60)*(T-60))-K1*A(1) Althought it makes no difference to your model it would be clearer to remove TM=T and change the expression for RIN so that it uses T rather than TIME e.g. > $DES > RIN=0.1+AMPL*0.1*COS((2*3.14159265/60)*(T-60)) > DADT(1)=RIN -K1*A(1) I suspect you are using TM and RIN to try to capture the valeus of T and RIN during integration but this will not work. You can only determine RIN and save it in a table at the time of an event in your data file. TM will always be the time at the end of the integration interval. There are two parameters in your model which you code as constants -- the period and phase. You have the phase with the same value as the period. There is no point in doing this > RIN=0.1+AMPL*0.1*COS((2*3.14159265/60)*(T-60)) and > RIN=0.1+AMPL*0.1*COS((2*3.14159265/60)*T) are equivalent. I used the following code to estimate period and phase and the run converged with 7 sig digs using ADVAN6. I would not recommend using ADVAN8 unless you have very good reason to suspect a stiff system (and I can see no evidence of that in your problem). $PROB TIME-CONTROLLED DRUG DELIVERY, SINGLE SUBJECT ;RESULTS ARE QUITE DIFFERENT WHEN I SPECIFY MISSING ;RECORD FOT TIME=0. STRANGE... $INPUT ID TIME DV $DATA data.txt $SUBROUTINES ADVAN6 TOL=7 ;TOL - THE NUMBER OF ACCURATE DIGITS $MODEL COMP=(DEPOT) $EST MAXEVAL=9990 SIG=7 PRINT=5 $COV ;COVARIANCE STEP IS IMPLEMENTED $THETA (.01,1.34,10) ;AMPL (.1,2.19,10) ;V1 (.001,0.0206,100) ;K1 (1,49.,100) ; PERIOD (-1,9.51,60) ; PHASE $OMEGA 0 FIXED ; Make NONMEM think this is a popln analysis but with single subject data $SIGMA 0.106 ;$OMEGA DIAGONAL(7) .1 .1 .1 .1 .1 .1 .1 $PK AMPL =THETA(1)*EXP(ETA(1)) ;AMPLITUDE OF OSCILATIONS V1 =THETA(2) ;VOLUME OF DISTRIBUTION; K1 =THETA(3) PERIOD=THETA(4) PHASE=THETA(5) S1 =V1 ;The amount A in the observation compartment ;at the time of observation, divided by the ;value of a parameter S, is used as the prediction. CL=K1*V1 $DES RIN=0.1+AMPL*0.1*COS((2*3.14159265/PERIOD)*(T-PHASE)) DADT(1)=RIN-K1*A(1) $ERROR Y=F+ERR(1) CONC=F $TABLE ID TIME AMPL V1 K1 CL Y NOPRINT FILE=cosine.fit Nick -- Zip file attachments have .gz extension. Please save as .zip http://www.health.auckland.ac.nz/pharmacology/staff/nholford/zip_attachment.htm **** 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/