Trough concentrations and ADDL

I am a new NONMEM user and have a simple question regarding the input file. I am analyzing trough concentrations in a multiple oral dose study. 20 trough concentrations are available per patient over a period of 10-12 weeks. The dose is frequently changing due to TDM. I wonder how it is recommended to code the dosing history in the inputfile effectively in this situation. I'm considering using ADDL, but am unfamiliar with it and unsure if I am using it correctly. This is a selected part of the inputfile: ID DAT1=DROP TIME EVID C=DV DOSE II ADDL 1 *01.01.2008* 20 1 0 4 12 4 1 *03.01.2008* 8 0 6,1 0 0 0 1 *04.01.2008* 8 0 7,6 0 0 0 1 *04.01.2008* 8 1 0 4 0 0 1 *04.01.2008* 20 1 0 3 12 12 1 *06.01.2008* 8 0 5,4 0 0 0 1 * 08.01.2008* 8 0 5,6 0 0 0 1 *11.01.2001* 8 0 4,4 0 0 0 1 *11.01.2008* 8 1 0 3 0 0 1 *11.01.2008* 20 1 0 3,5 12 20 1 *13.01.2008* 8 0 5,0 0 0 0 Is this similar to the way other nmusers use the ADDL item? Will NONMEM analyze the above data file with the same results, compared to this more simple, but less effective code (only first records): ID DAT1=DROP TIME EVID C=DV DOSE 1 *01.01.2008* 20 1 0 4 1 *02.01.2008* 8 1 0 4 1 *02.01.2008* 20 1 0 4 1 *03.01.2008* 8 0 6,1 0 1 *03.01.2008* 8 1 0 4 1 *03.01.2008* 20 1 0 4 1 *04.01.2008* 8 0 7,6 0 1 *04.01.2008* 8 1 0 4 1 *04.01.2008* 20 1 0 3 1 *05.01.2008* 8 1 0 3 1 *05.01.2008* 20 1 0 3 When doing the top approach, I have to calculate the number of doses to fill the ADDL item, which can be complicated if the time before the dose is changed is several weeks. This could give errors. Is there a way NONMEM could understand that "the patient will use this dose at 12 hour intervall until a new dose record is stated"? Thank you in advance for helping! Kindly regards Elisabet Størset, new nonmemuser.