I am trying to institute a time dependent Ka term (eg tvKa = (KaMax * time/(T50 + time)) to incorporate time dependent differences in absorption. I would like to use this over multiple dose regimens to explore variability in T50 as a function of occasion as it appears there are occasional differences in absorption lag and using the change point Tlag is unstable in estimating both intra and interindividual variability. As parameterized now, the model would only give the time dependence of the of the first dose. Subsequent doses would correspond to a tvKa approaching Kamax because this will not reset the time counter. Note I am employing a simple time counter in the dataset.
So my question is, how does one reset the time counter. Based on the manual, I understand this to be specified in a reset column where reset is specified along with a dose to reset the counter. Is this assumption correct?
My second question, if set the repeat dose regimen with II and ADDL, am I able to reset the time counter at every dose specified in ADDL? Or did I need to specify the doses long hand (i.e. a dose listed on every line where I want to reset the counter).
I am attaching a project (last model) that I hope will help you.
I added a baseline for Ka to avoid Ka=0 at t=0.
IN theory you can do it easily because at a dosepoint you can reset any state variable (the left part of the differential equation).
The idea is that derive(tsld=1) will give you without any reset the real time. Now if you tell after each dose to reset tsld to 0, you will get tsld reset to 0 and then cumulating til the next dose.
Because in th stparm you have a non conventional equation, I used the group statement where I put your special tvKa there.
For the second question, you can set repeating dosing using ADDL and II. See attached image: for row 1 it will be interpreted as a dose of 3750 will be given every 24 hours for 1 week.
