Dear Certara Team,
I was trying to model some data in which the patients have to take their drug daily but the PK sampling was done on sparse visits (2 visits only and in each PK visit there are average of 4 time points plus the predose drug level). there is an average of one month between each PK visit. it is Not crossover as the patients is taking the same drug daily. also the patients are on steady state because when they come to the first PK visit, they were almost on the drug for about 3 weeks.
so when i prepared the data, I flagged the steady state condition and i also used the ADDL to let the software know that there are additional doses until the second PK visit.
however, I don't know if i should use the reset option to overlay the data of the first and the second visits.
when i did that, i got higher AIC but the shape of the CWRES vs IVAR was improved.
so is it recommended here to use the reset option?
also, many times when i run the model i get failure of execution message for a given id. I used to get it very frequent before I sort the steady state and the ADDL. however, now i get it sometimes (less frequent) and I am not sure why. most of the time when change the way the dose variable is displayed or the way the ADDL is displayed, i can get some results but this is confusing because i don't know why. and does the initial estimates values (if they are not precise) can lead to model excution failure?
I am attaching the excel file example to show how did i sort the time, the steady state and the ADDL. I apologize that there are many columns for each but i tried different ways of sorting. all of them are based on the id and the PK visit number.
note that the patients are using different doses for the same drug (do i need to sort by the dose when i model?)
thank you very much